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Date: Wed, 15 Nov 2017 08:44:56 +0100
From: "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
Boqun Feng <boqun.feng@...il.com>,
Andy Lutomirski <luto@...capital.net>,
Dave Watson <davejwatson@...com>,
lkml <linux-kernel@...r.kernel.org>,
Linux API <linux-api@...r.kernel.org>,
Paul Turner <pjt@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Russell King <linux@....linux.org.uk>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H . Peter Anvin" <hpa@...or.com>, Andrew Hunter <ahh@...gle.com>,
Andi Kleen <andi@...stfloor.org>, Chris Lameter <cl@...ux.com>,
Ben Maurer <bmaurer@...com>,
Steven Rostedt <rostedt@...dmis.org>,
Josh Triplett <josh@...htriplett.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>
Subject: Re: [RFC PATCH v3 for 4.15 08/24] Provide cpu_opv system call
Hi Matthieu
On 14 November 2017 at 21:03, Mathieu Desnoyers
<mathieu.desnoyers@...icios.com> wrote:
> This new cpu_opv system call executes a vector of operations on behalf
> of user-space on a specific CPU with preemption disabled. It is inspired
> from readv() and writev() system calls which take a "struct iovec" array
> as argument.
Do you have a man page spfr this syscall already?
Thanks,
Michael
> The operations available are: comparison, memcpy, add, or, and, xor,
> left shift, right shift, and mb. The system call receives a CPU number
> from user-space as argument, which is the CPU on which those operations
> need to be performed. All preparation steps such as loading pointers,
> and applying offsets to arrays, need to be performed by user-space
> before invoking the system call. The "comparison" operation can be used
> to check that the data used in the preparation step did not change
> between preparation of system call inputs and operation execution within
> the preempt-off critical section.
>
> The reason why we require all pointer offsets to be calculated by
> user-space beforehand is because we need to use get_user_pages_fast() to
> first pin all pages touched by each operation. This takes care of
> faulting-in the pages. Then, preemption is disabled, and the operations
> are performed atomically with respect to other thread execution on that
> CPU, without generating any page fault.
>
> A maximum limit of 16 operations per cpu_opv syscall invocation is
> enforced, so user-space cannot generate a too long preempt-off critical
> section. Each operation is also limited a length of PAGE_SIZE bytes,
> meaning that an operation can touch a maximum of 4 pages (memcpy: 2
> pages for source, 2 pages for destination if addresses are not aligned
> on page boundaries). Moreover, a total limit of 4216 bytes is applied
> to operation lengths.
>
> If the thread is not running on the requested CPU, a new
> push_task_to_cpu() is invoked to migrate the task to the requested CPU.
> If the requested CPU is not part of the cpus allowed mask of the thread,
> the system call fails with EINVAL. After the migration has been
> performed, preemption is disabled, and the current CPU number is checked
> again and compared to the requested CPU number. If it still differs, it
> means the scheduler migrated us away from that CPU. Return EAGAIN to
> user-space in that case, and let user-space retry (either requesting the
> same CPU number, or a different one, depending on the user-space
> algorithm constraints).
>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> CC: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> CC: Peter Zijlstra <peterz@...radead.org>
> CC: Paul Turner <pjt@...gle.com>
> CC: Thomas Gleixner <tglx@...utronix.de>
> CC: Andrew Hunter <ahh@...gle.com>
> CC: Andy Lutomirski <luto@...capital.net>
> CC: Andi Kleen <andi@...stfloor.org>
> CC: Dave Watson <davejwatson@...com>
> CC: Chris Lameter <cl@...ux.com>
> CC: Ingo Molnar <mingo@...hat.com>
> CC: "H. Peter Anvin" <hpa@...or.com>
> CC: Ben Maurer <bmaurer@...com>
> CC: Steven Rostedt <rostedt@...dmis.org>
> CC: Josh Triplett <josh@...htriplett.org>
> CC: Linus Torvalds <torvalds@...ux-foundation.org>
> CC: Andrew Morton <akpm@...ux-foundation.org>
> CC: Russell King <linux@....linux.org.uk>
> CC: Catalin Marinas <catalin.marinas@....com>
> CC: Will Deacon <will.deacon@....com>
> CC: Michael Kerrisk <mtk.manpages@...il.com>
> CC: Boqun Feng <boqun.feng@...il.com>
> CC: linux-api@...r.kernel.org
> ---
>
> Changes since v1:
> - handle CPU hotplug,
> - cleanup implementation using function pointers: We can use function
> pointers to implement the operations rather than duplicating all the
> user-access code.
> - refuse device pages: Performing cpu_opv operations on io map'd pages
> with preemption disabled could generate long preempt-off critical
> sections, which leads to unwanted scheduler latency. Return EFAULT if
> a device page is received as parameter
> - restrict op vector to 4216 bytes length sum: Restrict the operation
> vector to length sum of:
> - 4096 bytes (typical page size on most architectures, should be
> enough for a string, or structures)
> - 15 * 8 bytes (typical operations on integers or pointers).
> The goal here is to keep the duration of preempt off critical section
> short, so we don't add significant scheduler latency.
> - Add INIT_ONSTACK macro: Introduce the
> CPU_OP_FIELD_u32_u64_INIT_ONSTACK() macros to ensure that users
> correctly initialize the upper bits of CPU_OP_FIELD_u32_u64() on their
> stack to 0 on 32-bit architectures.
> - Add CPU_MB_OP operation:
> Use-cases with:
> - two consecutive stores,
> - a mempcy followed by a store,
> require a memory barrier before the final store operation. A typical
> use-case is a store-release on the final store. Given that this is a
> slow path, just providing an explicit full barrier instruction should
> be sufficient.
> - Add expect fault field:
> The use-case of list_pop brings interesting challenges. With rseq, we
> can use rseq_cmpnev_storeoffp_load(), and therefore load a pointer,
> compare it against NULL, add an offset, and load the target "next"
> pointer from the object, all within a single req critical section.
>
> Life is not so easy for cpu_opv in this use-case, mainly because we
> need to pin all pages we are going to touch in the preempt-off
> critical section beforehand. So we need to know the target object (in
> which we apply an offset to fetch the next pointer) when we pin pages
> before disabling preemption.
>
> So the approach is to load the head pointer and compare it against
> NULL in user-space, before doing the cpu_opv syscall. User-space can
> then compute the address of the head->next field, *without loading it*.
>
> The cpu_opv system call will first need to pin all pages associated
> with input data. This includes the page backing the head->next object,
> which may have been concurrently deallocated and unmapped. Therefore,
> in this case, getting -EFAULT when trying to pin those pages may
> happen: it just means they have been concurrently unmapped. This is
> an expected situation, and should just return -EAGAIN to user-space,
> to user-space can distinguish between "should retry" type of
> situations and actual errors that should be handled with extreme
> prejudice to the program (e.g. abort()).
>
> Therefore, add "expect_fault" fields along with op input address
> pointers, so user-space can identify whether a fault when getting a
> field should return EAGAIN rather than EFAULT.
> - Add compiler barrier between operations: Adding a compiler barrier
> between store operations in a cpu_opv sequence can be useful when
> paired with membarrier system call.
>
> An algorithm with a paired slow path and fast path can use
> sys_membarrier on the slow path to replace fast-path memory barriers
> by compiler barrier.
>
> Adding an explicit compiler barrier between operations allows
> cpu_opv to be used as fallback for operations meant to match
> the membarrier system call.
>
> Changes since v2:
>
> - Fix memory leak by introducing struct cpu_opv_pinned_pages.
> Suggested by Boqun Feng.
> - Cast argument 1 passed to access_ok from integer to void __user *,
> fixing sparse warning.
> ---
> MAINTAINERS | 7 +
> include/uapi/linux/cpu_opv.h | 117 ++++++
> init/Kconfig | 14 +
> kernel/Makefile | 1 +
> kernel/cpu_opv.c | 968 +++++++++++++++++++++++++++++++++++++++++++
> kernel/sched/core.c | 37 ++
> kernel/sched/sched.h | 2 +
> kernel/sys_ni.c | 1 +
> 8 files changed, 1147 insertions(+)
> create mode 100644 include/uapi/linux/cpu_opv.h
> create mode 100644 kernel/cpu_opv.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index c9f95f8b07ed..45a1bbdaa287 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -3675,6 +3675,13 @@ B: https://bugzilla.kernel.org
> F: drivers/cpuidle/*
> F: include/linux/cpuidle.h
>
> +CPU NON-PREEMPTIBLE OPERATION VECTOR SUPPORT
> +M: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> +L: linux-kernel@...r.kernel.org
> +S: Supported
> +F: kernel/cpu_opv.c
> +F: include/uapi/linux/cpu_opv.h
> +
> CRAMFS FILESYSTEM
> W: http://sourceforge.net/projects/cramfs/
> S: Orphan / Obsolete
> diff --git a/include/uapi/linux/cpu_opv.h b/include/uapi/linux/cpu_opv.h
> new file mode 100644
> index 000000000000..17f7d46e053b
> --- /dev/null
> +++ b/include/uapi/linux/cpu_opv.h
> @@ -0,0 +1,117 @@
> +#ifndef _UAPI_LINUX_CPU_OPV_H
> +#define _UAPI_LINUX_CPU_OPV_H
> +
> +/*
> + * linux/cpu_opv.h
> + *
> + * CPU preempt-off operation vector system call API
> + *
> + * Copyright (c) 2017 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> + *
> + * Permission is hereby granted, free of charge, to any person obtaining a copy
> + * of this software and associated documentation files (the "Software"), to deal
> + * in the Software without restriction, including without limitation the rights
> + * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
> + * copies of the Software, and to permit persons to whom the Software is
> + * furnished to do so, subject to the following conditions:
> + *
> + * The above copyright notice and this permission notice shall be included in
> + * all copies or substantial portions of the Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
> + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
> + * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
> + * SOFTWARE.
> + */
> +
> +#ifdef __KERNEL__
> +# include <linux/types.h>
> +#else /* #ifdef __KERNEL__ */
> +# include <stdint.h>
> +#endif /* #else #ifdef __KERNEL__ */
> +
> +#include <asm/byteorder.h>
> +
> +#ifdef __LP64__
> +# define CPU_OP_FIELD_u32_u64(field) uint64_t field
> +# define CPU_OP_FIELD_u32_u64_INIT_ONSTACK(field, v) field = (intptr_t)v
> +#elif defined(__BYTE_ORDER) ? \
> + __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
> +# define CPU_OP_FIELD_u32_u64(field) uint32_t field ## _padding, field
> +# define CPU_OP_FIELD_u32_u64_INIT_ONSTACK(field, v) \
> + field ## _padding = 0, field = (intptr_t)v
> +#else
> +# define CPU_OP_FIELD_u32_u64(field) uint32_t field, field ## _padding
> +# define CPU_OP_FIELD_u32_u64_INIT_ONSTACK(field, v) \
> + field = (intptr_t)v, field ## _padding = 0
> +#endif
> +
> +#define CPU_OP_VEC_LEN_MAX 16
> +#define CPU_OP_ARG_LEN_MAX 24
> +/* Max. data len per operation. */
> +#define CPU_OP_DATA_LEN_MAX PAGE_SIZE
> +/*
> + * Max. data len for overall vector. We to restrict the amount of
> + * user-space data touched by the kernel in non-preemptible context so
> + * we do not introduce long scheduler latencies.
> + * This allows one copy of up to 4096 bytes, and 15 operations touching
> + * 8 bytes each.
> + * This limit is applied to the sum of length specified for all
> + * operations in a vector.
> + */
> +#define CPU_OP_VEC_DATA_LEN_MAX (4096 + 15*8)
> +#define CPU_OP_MAX_PAGES 4 /* Max. pages per op. */
> +
> +enum cpu_op_type {
> + CPU_COMPARE_EQ_OP, /* compare */
> + CPU_COMPARE_NE_OP, /* compare */
> + CPU_MEMCPY_OP, /* memcpy */
> + CPU_ADD_OP, /* arithmetic */
> + CPU_OR_OP, /* bitwise */
> + CPU_AND_OP, /* bitwise */
> + CPU_XOR_OP, /* bitwise */
> + CPU_LSHIFT_OP, /* shift */
> + CPU_RSHIFT_OP, /* shift */
> + CPU_MB_OP, /* memory barrier */
> +};
> +
> +/* Vector of operations to perform. Limited to 16. */
> +struct cpu_op {
> + int32_t op; /* enum cpu_op_type. */
> + uint32_t len; /* data length, in bytes. */
> + union {
> + struct {
> + CPU_OP_FIELD_u32_u64(a);
> + CPU_OP_FIELD_u32_u64(b);
> + uint8_t expect_fault_a;
> + uint8_t expect_fault_b;
> + } compare_op;
> + struct {
> + CPU_OP_FIELD_u32_u64(dst);
> + CPU_OP_FIELD_u32_u64(src);
> + uint8_t expect_fault_dst;
> + uint8_t expect_fault_src;
> + } memcpy_op;
> + struct {
> + CPU_OP_FIELD_u32_u64(p);
> + int64_t count;
> + uint8_t expect_fault_p;
> + } arithmetic_op;
> + struct {
> + CPU_OP_FIELD_u32_u64(p);
> + uint64_t mask;
> + uint8_t expect_fault_p;
> + } bitwise_op;
> + struct {
> + CPU_OP_FIELD_u32_u64(p);
> + uint32_t bits;
> + uint8_t expect_fault_p;
> + } shift_op;
> + char __padding[CPU_OP_ARG_LEN_MAX];
> + } u;
> +};
> +
> +#endif /* _UAPI_LINUX_CPU_OPV_H */
> diff --git a/init/Kconfig b/init/Kconfig
> index cbedfb91b40a..e4fbb5dd6a24 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1404,6 +1404,7 @@ config RSEQ
> bool "Enable rseq() system call" if EXPERT
> default y
> depends on HAVE_RSEQ
> + select CPU_OPV
> select MEMBARRIER
> help
> Enable the restartable sequences system call. It provides a
> @@ -1414,6 +1415,19 @@ config RSEQ
>
> If unsure, say Y.
>
> +config CPU_OPV
> + bool "Enable cpu_opv() system call" if EXPERT
> + default y
> + help
> + Enable the CPU preempt-off operation vector system call.
> + It allows user-space to perform a sequence of operations on
> + per-cpu data with preemption disabled. Useful as
> + single-stepping fall-back for restartable sequences, and for
> + performing more complex operations on per-cpu data that would
> + not be otherwise possible to do with restartable sequences.
> +
> + If unsure, say Y.
> +
> config EMBEDDED
> bool "Embedded system"
> option allnoconfig_y
> diff --git a/kernel/Makefile b/kernel/Makefile
> index 3574669dafd9..cac8855196ff 100644
> --- a/kernel/Makefile
> +++ b/kernel/Makefile
> @@ -113,6 +113,7 @@ obj-$(CONFIG_TORTURE_TEST) += torture.o
>
> obj-$(CONFIG_HAS_IOMEM) += memremap.o
> obj-$(CONFIG_RSEQ) += rseq.o
> +obj-$(CONFIG_CPU_OPV) += cpu_opv.o
>
> $(obj)/configs.o: $(obj)/config_data.h
>
> diff --git a/kernel/cpu_opv.c b/kernel/cpu_opv.c
> new file mode 100644
> index 000000000000..a81837a14b17
> --- /dev/null
> +++ b/kernel/cpu_opv.c
> @@ -0,0 +1,968 @@
> +/*
> + * CPU preempt-off operation vector system call
> + *
> + * It allows user-space to perform a sequence of operations on per-cpu
> + * data with preemption disabled. Useful as single-stepping fall-back
> + * for restartable sequences, and for performing more complex operations
> + * on per-cpu data that would not be otherwise possible to do with
> + * restartable sequences.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * Copyright (C) 2017, EfficiOS Inc.,
> + * Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> + */
> +
> +#include <linux/sched.h>
> +#include <linux/uaccess.h>
> +#include <linux/syscalls.h>
> +#include <linux/cpu_opv.h>
> +#include <linux/types.h>
> +#include <linux/mutex.h>
> +#include <linux/pagemap.h>
> +#include <asm/ptrace.h>
> +#include <asm/byteorder.h>
> +
> +#include "sched/sched.h"
> +
> +#define TMP_BUFLEN 64
> +#define NR_PINNED_PAGES_ON_STACK 8
> +
> +union op_fn_data {
> + uint8_t _u8;
> + uint16_t _u16;
> + uint32_t _u32;
> + uint64_t _u64;
> +#if (BITS_PER_LONG < 64)
> + uint32_t _u64_split[2];
> +#endif
> +};
> +
> +struct cpu_opv_pinned_pages {
> + struct page **pages;
> + size_t nr;
> + bool is_kmalloc;
> +};
> +
> +typedef int (*op_fn_t)(union op_fn_data *data, uint64_t v, uint32_t len);
> +
> +static DEFINE_MUTEX(cpu_opv_offline_lock);
> +
> +/*
> + * The cpu_opv system call executes a vector of operations on behalf of
> + * user-space on a specific CPU with preemption disabled. It is inspired
> + * from readv() and writev() system calls which take a "struct iovec"
> + * array as argument.
> + *
> + * The operations available are: comparison, memcpy, add, or, and, xor,
> + * left shift, and right shift. The system call receives a CPU number
> + * from user-space as argument, which is the CPU on which those
> + * operations need to be performed. All preparation steps such as
> + * loading pointers, and applying offsets to arrays, need to be
> + * performed by user-space before invoking the system call. The
> + * "comparison" operation can be used to check that the data used in the
> + * preparation step did not change between preparation of system call
> + * inputs and operation execution within the preempt-off critical
> + * section.
> + *
> + * The reason why we require all pointer offsets to be calculated by
> + * user-space beforehand is because we need to use get_user_pages_fast()
> + * to first pin all pages touched by each operation. This takes care of
> + * faulting-in the pages. Then, preemption is disabled, and the
> + * operations are performed atomically with respect to other thread
> + * execution on that CPU, without generating any page fault.
> + *
> + * A maximum limit of 16 operations per cpu_opv syscall invocation is
> + * enforced, and a overall maximum length sum, so user-space cannot
> + * generate a too long preempt-off critical section. Each operation is
> + * also limited a length of PAGE_SIZE bytes, meaning that an operation
> + * can touch a maximum of 4 pages (memcpy: 2 pages for source, 2 pages
> + * for destination if addresses are not aligned on page boundaries).
> + *
> + * If the thread is not running on the requested CPU, a new
> + * push_task_to_cpu() is invoked to migrate the task to the requested
> + * CPU. If the requested CPU is not part of the cpus allowed mask of
> + * the thread, the system call fails with EINVAL. After the migration
> + * has been performed, preemption is disabled, and the current CPU
> + * number is checked again and compared to the requested CPU number. If
> + * it still differs, it means the scheduler migrated us away from that
> + * CPU. Return EAGAIN to user-space in that case, and let user-space
> + * retry (either requesting the same CPU number, or a different one,
> + * depending on the user-space algorithm constraints).
> + */
> +
> +/*
> + * Check operation types and length parameters.
> + */
> +static int cpu_opv_check(struct cpu_op *cpuop, int cpuopcnt)
> +{
> + int i;
> + uint32_t sum = 0;
> +
> + for (i = 0; i < cpuopcnt; i++) {
> + struct cpu_op *op = &cpuop[i];
> +
> + switch (op->op) {
> + case CPU_MB_OP:
> + break;
> + default:
> + sum += op->len;
> + }
> + switch (op->op) {
> + case CPU_COMPARE_EQ_OP:
> + case CPU_COMPARE_NE_OP:
> + case CPU_MEMCPY_OP:
> + if (op->len > CPU_OP_DATA_LEN_MAX)
> + return -EINVAL;
> + break;
> + case CPU_ADD_OP:
> + case CPU_OR_OP:
> + case CPU_AND_OP:
> + case CPU_XOR_OP:
> + switch (op->len) {
> + case 1:
> + case 2:
> + case 4:
> + case 8:
> + break;
> + default:
> + return -EINVAL;
> + }
> + break;
> + case CPU_LSHIFT_OP:
> + case CPU_RSHIFT_OP:
> + switch (op->len) {
> + case 1:
> + if (op->u.shift_op.bits > 7)
> + return -EINVAL;
> + break;
> + case 2:
> + if (op->u.shift_op.bits > 15)
> + return -EINVAL;
> + break;
> + case 4:
> + if (op->u.shift_op.bits > 31)
> + return -EINVAL;
> + break;
> + case 8:
> + if (op->u.shift_op.bits > 63)
> + return -EINVAL;
> + break;
> + default:
> + return -EINVAL;
> + }
> + break;
> + case CPU_MB_OP:
> + break;
> + default:
> + return -EINVAL;
> + }
> + }
> + if (sum > CPU_OP_VEC_DATA_LEN_MAX)
> + return -EINVAL;
> + return 0;
> +}
> +
> +static unsigned long cpu_op_range_nr_pages(unsigned long addr,
> + unsigned long len)
> +{
> + return ((addr + len - 1) >> PAGE_SHIFT) - (addr >> PAGE_SHIFT) + 1;
> +}
> +
> +static int cpu_op_check_page(struct page *page)
> +{
> + struct address_space *mapping;
> +
> + if (is_zone_device_page(page))
> + return -EFAULT;
> + page = compound_head(page);
> + mapping = READ_ONCE(page->mapping);
> + if (!mapping) {
> + int shmem_swizzled;
> +
> + /*
> + * Check again with page lock held to guard against
> + * memory pressure making shmem_writepage move the page
> + * from filecache to swapcache.
> + */
> + lock_page(page);
> + shmem_swizzled = PageSwapCache(page) || page->mapping;
> + unlock_page(page);
> + if (shmem_swizzled)
> + return -EAGAIN;
> + return -EFAULT;
> + }
> + return 0;
> +}
> +
> +/*
> + * Refusing device pages, the zero page, pages in the gate area, and
> + * special mappings. Inspired from futex.c checks.
> + */
> +static int cpu_op_check_pages(struct page **pages,
> + unsigned long nr_pages)
> +{
> + unsigned long i;
> +
> + for (i = 0; i < nr_pages; i++) {
> + int ret;
> +
> + ret = cpu_op_check_page(pages[i]);
> + if (ret)
> + return ret;
> + }
> + return 0;
> +}
> +
> +static int cpu_op_pin_pages(unsigned long addr, unsigned long len,
> + struct cpu_opv_pinned_pages *pin_pages, int write)
> +{
> + struct page *pages[2];
> + int ret, nr_pages;
> +
> + if (!len)
> + return 0;
> + nr_pages = cpu_op_range_nr_pages(addr, len);
> + BUG_ON(nr_pages > 2);
> + if (!pin_pages->is_kmalloc && pin_pages->nr + nr_pages
> + > NR_PINNED_PAGES_ON_STACK) {
> + struct page **pinned_pages =
> + kzalloc(CPU_OP_VEC_LEN_MAX * CPU_OP_MAX_PAGES
> + * sizeof(struct page *), GFP_KERNEL);
> + if (!pinned_pages)
> + return -ENOMEM;
> + memcpy(pinned_pages, pin_pages->pages,
> + pin_pages->nr * sizeof(struct page *));
> + pin_pages->pages = pinned_pages;
> + pin_pages->is_kmalloc = true;
> + }
> +again:
> + ret = get_user_pages_fast(addr, nr_pages, write, pages);
> + if (ret < nr_pages) {
> + if (ret > 0)
> + put_page(pages[0]);
> + return -EFAULT;
> + }
> + /*
> + * Refuse device pages, the zero page, pages in the gate area,
> + * and special mappings.
> + */
> + ret = cpu_op_check_pages(pages, nr_pages);
> + if (ret == -EAGAIN) {
> + put_page(pages[0]);
> + if (nr_pages > 1)
> + put_page(pages[1]);
> + goto again;
> + }
> + if (ret)
> + goto error;
> + pin_pages->pages[pin_pages->nr++] = pages[0];
> + if (nr_pages > 1)
> + pin_pages->pages[pin_pages->nr++] = pages[1];
> + return 0;
> +
> +error:
> + put_page(pages[0]);
> + if (nr_pages > 1)
> + put_page(pages[1]);
> + return -EFAULT;
> +}
> +
> +static int cpu_opv_pin_pages(struct cpu_op *cpuop, int cpuopcnt,
> + struct cpu_opv_pinned_pages *pin_pages)
> +{
> + int ret, i;
> + bool expect_fault = false;
> +
> + /* Check access, pin pages. */
> + for (i = 0; i < cpuopcnt; i++) {
> + struct cpu_op *op = &cpuop[i];
> +
> + switch (op->op) {
> + case CPU_COMPARE_EQ_OP:
> + case CPU_COMPARE_NE_OP:
> + ret = -EFAULT;
> + expect_fault = op->u.compare_op.expect_fault_a;
> + if (!access_ok(VERIFY_READ,
> + (void __user *)op->u.compare_op.a,
> + op->len))
> + goto error;
> + ret = cpu_op_pin_pages(
> + (unsigned long)op->u.compare_op.a,
> + op->len, pin_pages, 0);
> + if (ret)
> + goto error;
> + ret = -EFAULT;
> + expect_fault = op->u.compare_op.expect_fault_b;
> + if (!access_ok(VERIFY_READ,
> + (void __user *)op->u.compare_op.b,
> + op->len))
> + goto error;
> + ret = cpu_op_pin_pages(
> + (unsigned long)op->u.compare_op.b,
> + op->len, pin_pages, 0);
> + if (ret)
> + goto error;
> + break;
> + case CPU_MEMCPY_OP:
> + ret = -EFAULT;
> + expect_fault = op->u.memcpy_op.expect_fault_dst;
> + if (!access_ok(VERIFY_WRITE,
> + (void __user *)op->u.memcpy_op.dst,
> + op->len))
> + goto error;
> + ret = cpu_op_pin_pages(
> + (unsigned long)op->u.memcpy_op.dst,
> + op->len, pin_pages, 1);
> + if (ret)
> + goto error;
> + ret = -EFAULT;
> + expect_fault = op->u.memcpy_op.expect_fault_src;
> + if (!access_ok(VERIFY_READ,
> + (void __user *)op->u.memcpy_op.src,
> + op->len))
> + goto error;
> + ret = cpu_op_pin_pages(
> + (unsigned long)op->u.memcpy_op.src,
> + op->len, pin_pages, 0);
> + if (ret)
> + goto error;
> + break;
> + case CPU_ADD_OP:
> + ret = -EFAULT;
> + expect_fault = op->u.arithmetic_op.expect_fault_p;
> + if (!access_ok(VERIFY_WRITE,
> + (void __user *)op->u.arithmetic_op.p,
> + op->len))
> + goto error;
> + ret = cpu_op_pin_pages(
> + (unsigned long)op->u.arithmetic_op.p,
> + op->len, pin_pages, 1);
> + if (ret)
> + goto error;
> + break;
> + case CPU_OR_OP:
> + case CPU_AND_OP:
> + case CPU_XOR_OP:
> + ret = -EFAULT;
> + expect_fault = op->u.bitwise_op.expect_fault_p;
> + if (!access_ok(VERIFY_WRITE,
> + (void __user *)op->u.bitwise_op.p,
> + op->len))
> + goto error;
> + ret = cpu_op_pin_pages(
> + (unsigned long)op->u.bitwise_op.p,
> + op->len, pin_pages, 1);
> + if (ret)
> + goto error;
> + break;
> + case CPU_LSHIFT_OP:
> + case CPU_RSHIFT_OP:
> + ret = -EFAULT;
> + expect_fault = op->u.shift_op.expect_fault_p;
> + if (!access_ok(VERIFY_WRITE,
> + (void __user *)op->u.shift_op.p,
> + op->len))
> + goto error;
> + ret = cpu_op_pin_pages(
> + (unsigned long)op->u.shift_op.p,
> + op->len, pin_pages, 1);
> + if (ret)
> + goto error;
> + break;
> + case CPU_MB_OP:
> + break;
> + default:
> + return -EINVAL;
> + }
> + }
> + return 0;
> +
> +error:
> + for (i = 0; i < pin_pages->nr; i++)
> + put_page(pin_pages->pages[i]);
> + pin_pages->nr = 0;
> + /*
> + * If faulting access is expected, return EAGAIN to user-space.
> + * It allows user-space to distinguish between a fault caused by
> + * an access which is expect to fault (e.g. due to concurrent
> + * unmapping of underlying memory) from an unexpected fault from
> + * which a retry would not recover.
> + */
> + if (ret == -EFAULT && expect_fault)
> + return -EAGAIN;
> + return ret;
> +}
> +
> +/* Return 0 if same, > 0 if different, < 0 on error. */
> +static int do_cpu_op_compare_iter(void __user *a, void __user *b, uint32_t len)
> +{
> + char bufa[TMP_BUFLEN], bufb[TMP_BUFLEN];
> + uint32_t compared = 0;
> +
> + while (compared != len) {
> + unsigned long to_compare;
> +
> + to_compare = min_t(uint32_t, TMP_BUFLEN, len - compared);
> + if (__copy_from_user_inatomic(bufa, a + compared, to_compare))
> + return -EFAULT;
> + if (__copy_from_user_inatomic(bufb, b + compared, to_compare))
> + return -EFAULT;
> + if (memcmp(bufa, bufb, to_compare))
> + return 1; /* different */
> + compared += to_compare;
> + }
> + return 0; /* same */
> +}
> +
> +/* Return 0 if same, > 0 if different, < 0 on error. */
> +static int do_cpu_op_compare(void __user *a, void __user *b, uint32_t len)
> +{
> + int ret = -EFAULT;
> + union {
> + uint8_t _u8;
> + uint16_t _u16;
> + uint32_t _u32;
> + uint64_t _u64;
> +#if (BITS_PER_LONG < 64)
> + uint32_t _u64_split[2];
> +#endif
> + } tmp[2];
> +
> + pagefault_disable();
> + switch (len) {
> + case 1:
> + if (__get_user(tmp[0]._u8, (uint8_t __user *)a))
> + goto end;
> + if (__get_user(tmp[1]._u8, (uint8_t __user *)b))
> + goto end;
> + ret = !!(tmp[0]._u8 != tmp[1]._u8);
> + break;
> + case 2:
> + if (__get_user(tmp[0]._u16, (uint16_t __user *)a))
> + goto end;
> + if (__get_user(tmp[1]._u16, (uint16_t __user *)b))
> + goto end;
> + ret = !!(tmp[0]._u16 != tmp[1]._u16);
> + break;
> + case 4:
> + if (__get_user(tmp[0]._u32, (uint32_t __user *)a))
> + goto end;
> + if (__get_user(tmp[1]._u32, (uint32_t __user *)b))
> + goto end;
> + ret = !!(tmp[0]._u32 != tmp[1]._u32);
> + break;
> + case 8:
> +#if (BITS_PER_LONG >= 64)
> + if (__get_user(tmp[0]._u64, (uint64_t __user *)a))
> + goto end;
> + if (__get_user(tmp[1]._u64, (uint64_t __user *)b))
> + goto end;
> +#else
> + if (__get_user(tmp[0]._u64_split[0], (uint32_t __user *)a))
> + goto end;
> + if (__get_user(tmp[0]._u64_split[1], (uint32_t __user *)a + 1))
> + goto end;
> + if (__get_user(tmp[1]._u64_split[0], (uint32_t __user *)b))
> + goto end;
> + if (__get_user(tmp[1]._u64_split[1], (uint32_t __user *)b + 1))
> + goto end;
> +#endif
> + ret = !!(tmp[0]._u64 != tmp[1]._u64);
> + break;
> + default:
> + pagefault_enable();
> + return do_cpu_op_compare_iter(a, b, len);
> + }
> +end:
> + pagefault_enable();
> + return ret;
> +}
> +
> +/* Return 0 on success, < 0 on error. */
> +static int do_cpu_op_memcpy_iter(void __user *dst, void __user *src,
> + uint32_t len)
> +{
> + char buf[TMP_BUFLEN];
> + uint32_t copied = 0;
> +
> + while (copied != len) {
> + unsigned long to_copy;
> +
> + to_copy = min_t(uint32_t, TMP_BUFLEN, len - copied);
> + if (__copy_from_user_inatomic(buf, src + copied, to_copy))
> + return -EFAULT;
> + if (__copy_to_user_inatomic(dst + copied, buf, to_copy))
> + return -EFAULT;
> + copied += to_copy;
> + }
> + return 0;
> +}
> +
> +/* Return 0 on success, < 0 on error. */
> +static int do_cpu_op_memcpy(void __user *dst, void __user *src, uint32_t len)
> +{
> + int ret = -EFAULT;
> + union {
> + uint8_t _u8;
> + uint16_t _u16;
> + uint32_t _u32;
> + uint64_t _u64;
> +#if (BITS_PER_LONG < 64)
> + uint32_t _u64_split[2];
> +#endif
> + } tmp;
> +
> + pagefault_disable();
> + switch (len) {
> + case 1:
> + if (__get_user(tmp._u8, (uint8_t __user *)src))
> + goto end;
> + if (__put_user(tmp._u8, (uint8_t __user *)dst))
> + goto end;
> + break;
> + case 2:
> + if (__get_user(tmp._u16, (uint16_t __user *)src))
> + goto end;
> + if (__put_user(tmp._u16, (uint16_t __user *)dst))
> + goto end;
> + break;
> + case 4:
> + if (__get_user(tmp._u32, (uint32_t __user *)src))
> + goto end;
> + if (__put_user(tmp._u32, (uint32_t __user *)dst))
> + goto end;
> + break;
> + case 8:
> +#if (BITS_PER_LONG >= 64)
> + if (__get_user(tmp._u64, (uint64_t __user *)src))
> + goto end;
> + if (__put_user(tmp._u64, (uint64_t __user *)dst))
> + goto end;
> +#else
> + if (__get_user(tmp._u64_split[0], (uint32_t __user *)src))
> + goto end;
> + if (__get_user(tmp._u64_split[1], (uint32_t __user *)src + 1))
> + goto end;
> + if (__put_user(tmp._u64_split[0], (uint32_t __user *)dst))
> + goto end;
> + if (__put_user(tmp._u64_split[1], (uint32_t __user *)dst + 1))
> + goto end;
> +#endif
> + break;
> + default:
> + pagefault_enable();
> + return do_cpu_op_memcpy_iter(dst, src, len);
> + }
> + ret = 0;
> +end:
> + pagefault_enable();
> + return ret;
> +}
> +
> +static int op_add_fn(union op_fn_data *data, uint64_t count, uint32_t len)
> +{
> + int ret = 0;
> +
> + switch (len) {
> + case 1:
> + data->_u8 += (uint8_t)count;
> + break;
> + case 2:
> + data->_u16 += (uint16_t)count;
> + break;
> + case 4:
> + data->_u32 += (uint32_t)count;
> + break;
> + case 8:
> + data->_u64 += (uint64_t)count;
> + break;
> + default:
> + ret = -EINVAL;
> + break;
> + }
> + return ret;
> +}
> +
> +static int op_or_fn(union op_fn_data *data, uint64_t mask, uint32_t len)
> +{
> + int ret = 0;
> +
> + switch (len) {
> + case 1:
> + data->_u8 |= (uint8_t)mask;
> + break;
> + case 2:
> + data->_u16 |= (uint16_t)mask;
> + break;
> + case 4:
> + data->_u32 |= (uint32_t)mask;
> + break;
> + case 8:
> + data->_u64 |= (uint64_t)mask;
> + break;
> + default:
> + ret = -EINVAL;
> + break;
> + }
> + return ret;
> +}
> +
> +static int op_and_fn(union op_fn_data *data, uint64_t mask, uint32_t len)
> +{
> + int ret = 0;
> +
> + switch (len) {
> + case 1:
> + data->_u8 &= (uint8_t)mask;
> + break;
> + case 2:
> + data->_u16 &= (uint16_t)mask;
> + break;
> + case 4:
> + data->_u32 &= (uint32_t)mask;
> + break;
> + case 8:
> + data->_u64 &= (uint64_t)mask;
> + break;
> + default:
> + ret = -EINVAL;
> + break;
> + }
> + return ret;
> +}
> +
> +static int op_xor_fn(union op_fn_data *data, uint64_t mask, uint32_t len)
> +{
> + int ret = 0;
> +
> + switch (len) {
> + case 1:
> + data->_u8 ^= (uint8_t)mask;
> + break;
> + case 2:
> + data->_u16 ^= (uint16_t)mask;
> + break;
> + case 4:
> + data->_u32 ^= (uint32_t)mask;
> + break;
> + case 8:
> + data->_u64 ^= (uint64_t)mask;
> + break;
> + default:
> + ret = -EINVAL;
> + break;
> + }
> + return ret;
> +}
> +
> +static int op_lshift_fn(union op_fn_data *data, uint64_t bits, uint32_t len)
> +{
> + int ret = 0;
> +
> + switch (len) {
> + case 1:
> + data->_u8 <<= (uint8_t)bits;
> + break;
> + case 2:
> + data->_u16 <<= (uint16_t)bits;
> + break;
> + case 4:
> + data->_u32 <<= (uint32_t)bits;
> + break;
> + case 8:
> + data->_u64 <<= (uint64_t)bits;
> + break;
> + default:
> + ret = -EINVAL;
> + break;
> + }
> + return ret;
> +}
> +
> +static int op_rshift_fn(union op_fn_data *data, uint64_t bits, uint32_t len)
> +{
> + int ret = 0;
> +
> + switch (len) {
> + case 1:
> + data->_u8 >>= (uint8_t)bits;
> + break;
> + case 2:
> + data->_u16 >>= (uint16_t)bits;
> + break;
> + case 4:
> + data->_u32 >>= (uint32_t)bits;
> + break;
> + case 8:
> + data->_u64 >>= (uint64_t)bits;
> + break;
> + default:
> + ret = -EINVAL;
> + break;
> + }
> + return ret;
> +}
> +
> +/* Return 0 on success, < 0 on error. */
> +static int do_cpu_op_fn(op_fn_t op_fn, void __user *p, uint64_t v,
> + uint32_t len)
> +{
> + int ret = -EFAULT;
> + union op_fn_data tmp;
> +
> + pagefault_disable();
> + switch (len) {
> + case 1:
> + if (__get_user(tmp._u8, (uint8_t __user *)p))
> + goto end;
> + if (op_fn(&tmp, v, len))
> + goto end;
> + if (__put_user(tmp._u8, (uint8_t __user *)p))
> + goto end;
> + break;
> + case 2:
> + if (__get_user(tmp._u16, (uint16_t __user *)p))
> + goto end;
> + if (op_fn(&tmp, v, len))
> + goto end;
> + if (__put_user(tmp._u16, (uint16_t __user *)p))
> + goto end;
> + break;
> + case 4:
> + if (__get_user(tmp._u32, (uint32_t __user *)p))
> + goto end;
> + if (op_fn(&tmp, v, len))
> + goto end;
> + if (__put_user(tmp._u32, (uint32_t __user *)p))
> + goto end;
> + break;
> + case 8:
> +#if (BITS_PER_LONG >= 64)
> + if (__get_user(tmp._u64, (uint64_t __user *)p))
> + goto end;
> +#else
> + if (__get_user(tmp._u64_split[0], (uint32_t __user *)p))
> + goto end;
> + if (__get_user(tmp._u64_split[1], (uint32_t __user *)p + 1))
> + goto end;
> +#endif
> + if (op_fn(&tmp, v, len))
> + goto end;
> +#if (BITS_PER_LONG >= 64)
> + if (__put_user(tmp._u64, (uint64_t __user *)p))
> + goto end;
> +#else
> + if (__put_user(tmp._u64_split[0], (uint32_t __user *)p))
> + goto end;
> + if (__put_user(tmp._u64_split[1], (uint32_t __user *)p + 1))
> + goto end;
> +#endif
> + break;
> + default:
> + ret = -EINVAL;
> + goto end;
> + }
> + ret = 0;
> +end:
> + pagefault_enable();
> + return ret;
> +}
> +
> +static int __do_cpu_opv(struct cpu_op *cpuop, int cpuopcnt)
> +{
> + int i, ret;
> +
> + for (i = 0; i < cpuopcnt; i++) {
> + struct cpu_op *op = &cpuop[i];
> +
> + /* Guarantee a compiler barrier between each operation. */
> + barrier();
> +
> + switch (op->op) {
> + case CPU_COMPARE_EQ_OP:
> + ret = do_cpu_op_compare(
> + (void __user *)op->u.compare_op.a,
> + (void __user *)op->u.compare_op.b,
> + op->len);
> + /* Stop execution on error. */
> + if (ret < 0)
> + return ret;
> + /*
> + * Stop execution, return op index + 1 if comparison
> + * differs.
> + */
> + if (ret > 0)
> + return i + 1;
> + break;
> + case CPU_COMPARE_NE_OP:
> + ret = do_cpu_op_compare(
> + (void __user *)op->u.compare_op.a,
> + (void __user *)op->u.compare_op.b,
> + op->len);
> + /* Stop execution on error. */
> + if (ret < 0)
> + return ret;
> + /*
> + * Stop execution, return op index + 1 if comparison
> + * is identical.
> + */
> + if (ret == 0)
> + return i + 1;
> + break;
> + case CPU_MEMCPY_OP:
> + ret = do_cpu_op_memcpy(
> + (void __user *)op->u.memcpy_op.dst,
> + (void __user *)op->u.memcpy_op.src,
> + op->len);
> + /* Stop execution on error. */
> + if (ret)
> + return ret;
> + break;
> + case CPU_ADD_OP:
> + ret = do_cpu_op_fn(op_add_fn,
> + (void __user *)op->u.arithmetic_op.p,
> + op->u.arithmetic_op.count, op->len);
> + /* Stop execution on error. */
> + if (ret)
> + return ret;
> + break;
> + case CPU_OR_OP:
> + ret = do_cpu_op_fn(op_or_fn,
> + (void __user *)op->u.bitwise_op.p,
> + op->u.bitwise_op.mask, op->len);
> + /* Stop execution on error. */
> + if (ret)
> + return ret;
> + break;
> + case CPU_AND_OP:
> + ret = do_cpu_op_fn(op_and_fn,
> + (void __user *)op->u.bitwise_op.p,
> + op->u.bitwise_op.mask, op->len);
> + /* Stop execution on error. */
> + if (ret)
> + return ret;
> + break;
> + case CPU_XOR_OP:
> + ret = do_cpu_op_fn(op_xor_fn,
> + (void __user *)op->u.bitwise_op.p,
> + op->u.bitwise_op.mask, op->len);
> + /* Stop execution on error. */
> + if (ret)
> + return ret;
> + break;
> + case CPU_LSHIFT_OP:
> + ret = do_cpu_op_fn(op_lshift_fn,
> + (void __user *)op->u.shift_op.p,
> + op->u.shift_op.bits, op->len);
> + /* Stop execution on error. */
> + if (ret)
> + return ret;
> + break;
> + case CPU_RSHIFT_OP:
> + ret = do_cpu_op_fn(op_rshift_fn,
> + (void __user *)op->u.shift_op.p,
> + op->u.shift_op.bits, op->len);
> + /* Stop execution on error. */
> + if (ret)
> + return ret;
> + break;
> + case CPU_MB_OP:
> + smp_mb();
> + break;
> + default:
> + return -EINVAL;
> + }
> + }
> + return 0;
> +}
> +
> +static int do_cpu_opv(struct cpu_op *cpuop, int cpuopcnt, int cpu)
> +{
> + int ret;
> +
> + if (cpu != raw_smp_processor_id()) {
> + ret = push_task_to_cpu(current, cpu);
> + if (ret)
> + goto check_online;
> + }
> + preempt_disable();
> + if (cpu != smp_processor_id()) {
> + ret = -EAGAIN;
> + goto end;
> + }
> + ret = __do_cpu_opv(cpuop, cpuopcnt);
> +end:
> + preempt_enable();
> + return ret;
> +
> +check_online:
> + if (!cpu_possible(cpu))
> + return -EINVAL;
> + get_online_cpus();
> + if (cpu_online(cpu)) {
> + ret = -EAGAIN;
> + goto put_online_cpus;
> + }
> + /*
> + * CPU is offline. Perform operation from the current CPU with
> + * cpu_online read lock held, preventing that CPU from coming online,
> + * and with mutex held, providing mutual exclusion against other
> + * CPUs also finding out about an offline CPU.
> + */
> + mutex_lock(&cpu_opv_offline_lock);
> + ret = __do_cpu_opv(cpuop, cpuopcnt);
> + mutex_unlock(&cpu_opv_offline_lock);
> +put_online_cpus:
> + put_online_cpus();
> + return ret;
> +}
> +
> +/*
> + * cpu_opv - execute operation vector on a given CPU with preempt off.
> + *
> + * Userspace should pass current CPU number as parameter. May fail with
> + * -EAGAIN if currently executing on the wrong CPU.
> + */
> +SYSCALL_DEFINE4(cpu_opv, struct cpu_op __user *, ucpuopv, int, cpuopcnt,
> + int, cpu, int, flags)
> +{
> + struct cpu_op cpuopv[CPU_OP_VEC_LEN_MAX];
> + struct page *pinned_pages_on_stack[NR_PINNED_PAGES_ON_STACK];
> + struct cpu_opv_pinned_pages pin_pages = {
> + .pages = pinned_pages_on_stack,
> + .nr = 0,
> + .is_kmalloc = false,
> + };
> + int ret, i;
> +
> + if (unlikely(flags))
> + return -EINVAL;
> + if (unlikely(cpu < 0))
> + return -EINVAL;
> + if (cpuopcnt < 0 || cpuopcnt > CPU_OP_VEC_LEN_MAX)
> + return -EINVAL;
> + if (copy_from_user(cpuopv, ucpuopv, cpuopcnt * sizeof(struct cpu_op)))
> + return -EFAULT;
> + ret = cpu_opv_check(cpuopv, cpuopcnt);
> + if (ret)
> + return ret;
> + ret = cpu_opv_pin_pages(cpuopv, cpuopcnt, &pin_pages);
> + if (ret)
> + goto end;
> + ret = do_cpu_opv(cpuopv, cpuopcnt, cpu);
> + for (i = 0; i < pin_pages.nr; i++)
> + put_page(pin_pages.pages[i]);
> +end:
> + if (pin_pages.is_kmalloc)
> + kfree(pin_pages.pages);
> + return ret;
> +}
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 6bba05f47e51..e547f93a46c2 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1052,6 +1052,43 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
> set_curr_task(rq, p);
> }
>
> +int push_task_to_cpu(struct task_struct *p, unsigned int dest_cpu)
> +{
> + struct rq_flags rf;
> + struct rq *rq;
> + int ret = 0;
> +
> + rq = task_rq_lock(p, &rf);
> + update_rq_clock(rq);
> +
> + if (!cpumask_test_cpu(dest_cpu, &p->cpus_allowed)) {
> + ret = -EINVAL;
> + goto out;
> + }
> +
> + if (task_cpu(p) == dest_cpu)
> + goto out;
> +
> + if (task_running(rq, p) || p->state == TASK_WAKING) {
> + struct migration_arg arg = { p, dest_cpu };
> + /* Need help from migration thread: drop lock and wait. */
> + task_rq_unlock(rq, p, &rf);
> + stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg);
> + tlb_migrate_finish(p->mm);
> + return 0;
> + } else if (task_on_rq_queued(p)) {
> + /*
> + * OK, since we're going to drop the lock immediately
> + * afterwards anyway.
> + */
> + rq = move_queued_task(rq, &rf, p, dest_cpu);
> + }
> +out:
> + task_rq_unlock(rq, p, &rf);
> +
> + return ret;
> +}
> +
> /*
> * Change a given task's CPU affinity. Migrate the thread to a
> * proper CPU and schedule it away if the CPU it's executing on
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 3b448ba82225..cab256c1720a 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1209,6 +1209,8 @@ static inline void __set_task_cpu(struct task_struct *p, unsigned int cpu)
> #endif
> }
>
> +int push_task_to_cpu(struct task_struct *p, unsigned int dest_cpu);
> +
> /*
> * Tunables that become constants when CONFIG_SCHED_DEBUG is off:
> */
> diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> index bfa1ee1bf669..59e622296dc3 100644
> --- a/kernel/sys_ni.c
> +++ b/kernel/sys_ni.c
> @@ -262,3 +262,4 @@ cond_syscall(sys_pkey_free);
>
> /* restartable sequence */
> cond_syscall(sys_rseq);
> +cond_syscall(sys_cpu_opv);
> --
> 2.11.0
>
>
>
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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