Message-ID: <ef7f092c-2372-ddb7-7689-a9e6cbfe5334@loongson.cn>
Date:   Tue, 30 Aug 2022 12:07:48 +0800
From:   Jinyang He <hejinyang@...ngson.cn>
To:     Huacai Chen <chenhuacai@...nel.org>,
        Youling Tang <tangyouling@...ngson.cn>
Cc:     Baoquan He <bhe@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        WANG Xuerui <kernel@...0n.name>,
        Vivek Goyal <vgoyal@...hat.com>,
        Dave Young <dyoung@...hat.com>, Guo Ren <guoren@...nel.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        kexec@...ts.infradead.org, loongarch@...ts.linux.dev,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] LoongArch: Add kexec support

On 08/30/2022 11:42 AM, Huacai Chen wrote:

> On Tue, Aug 30, 2022 at 11:26 AM Youling Tang <tangyouling@...ngson.cn> wrote:
>> Hi, Jinyang
>>
>> On 08/30/2022 09:53 AM, Jinyang He wrote:
>>> Hi, Youling,
>>>
>>>
>>> On 08/29/2022 12:37 PM, Youling Tang wrote:
>>>> Add three new files, kexec.h, machine_kexec.c and relocate_kernel.S to
>>>> the
>>>> LoongArch architecture that add support for the kexec re-boot mechanis
>>>> (CONFIG_KEXEC) on LoongArch platforms.
>>>>
>>>> Supports loading vmlinux (vmlinux.elf) in ELF format and vmlinux.efi in
>>>> PE format.
>>>>
>>>> I tested this on  LoongArch 3A5000 machine and works as expected,
>>>>
>>>>    $ sudo kexec -l /boot/vmlinux.efi --reuse-cmdline
>>>>    $ sudo kexec -e
>>>>
>>>> Signed-off-by: Youling Tang <tangyouling@...ngson.cn>
>>>> ---
>>>>    arch/loongarch/Kconfig                  |  11 ++
>>>>    arch/loongarch/include/asm/kexec.h      |  58 ++++++++
>>>>    arch/loongarch/kernel/Makefile          |   2 +
>>>>    arch/loongarch/kernel/head.S            |   7 +-
>>>>    arch/loongarch/kernel/machine_kexec.c   | 178 ++++++++++++++++++++++++
>>>>    arch/loongarch/kernel/relocate_kernel.S | 125 +++++++++++++++++
>>>>    6 files changed, 380 insertions(+), 1 deletion(-)
>>>>    create mode 100644 arch/loongarch/include/asm/kexec.h
>>>>    create mode 100644 arch/loongarch/kernel/machine_kexec.c
>>>>    create mode 100644 arch/loongarch/kernel/relocate_kernel.S
>>>>
>>>> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
>>>> index 45364cffc793..903c82fa958d 100644
>>>> --- a/arch/loongarch/Kconfig
>>>> +++ b/arch/loongarch/Kconfig
>>>> @@ -409,6 +409,17 @@ config FORCE_MAX_ZONEORDER
>>>>          The page size is not necessarily 4KB.  Keep this in mind
>>>>          when choosing a value for this option.
>>>>    +config KEXEC
>>>> +    bool "Kexec system call"
>>>> +    select KEXEC_CORE
>>>> +    help
>>>> +      kexec is a system call that implements the ability to shutdown
>>>> your
>>>> +      current kernel, and to start another kernel.  It is like a reboot
>>>> +      but it is independent of the system firmware.   And like a reboot
>>>> +      you can start any kernel with it, not just Linux.
>>>> +
>>>> +      The name comes from the similarity to the exec system call.
>>>> +
>>>>    config SECCOMP
>>>>        bool "Enable seccomp to safely compute untrusted bytecode"
>>>>        depends on PROC_FS
>>>> diff --git a/arch/loongarch/include/asm/kexec.h
>>>> b/arch/loongarch/include/asm/kexec.h
>>>> new file mode 100644
>>>> index 000000000000..5c9e7b5eccb8
>>>> --- /dev/null
>>>> +++ b/arch/loongarch/include/asm/kexec.h
>>>> @@ -0,0 +1,58 @@
>>>> +/* SPDX-License-Identifier: GPL-2.0 */
>>>> +/*
>>>> + * kexec.h for kexec
>>>> + *
>>>> + * Copyright (C) 2022 Loongson Technology Corporation Limited
>>>> + */
>>>> +
>>>> +#ifndef _ASM_KEXEC_H
>>>> +#define _ASM_KEXEC_H
>>>> +
>>>> +#include <asm/stacktrace.h>
>>>> +#include <asm/page.h>
>>>> +
>>>> +/* Maximum physical address we can use pages from */
>>>> +#define KEXEC_SOURCE_MEMORY_LIMIT (-1UL)
>>>> +/* Maximum address we can reach in physical address mode */
>>>> +#define KEXEC_DESTINATION_MEMORY_LIMIT (-1UL)
>>>> + /* Maximum address we can use for the control code buffer */
>>>> +#define KEXEC_CONTROL_MEMORY_LIMIT (-1UL)
>>>> +
>>>> +/* Reserve a page for the control code buffer */
>>>> +#define KEXEC_CONTROL_PAGE_SIZE PAGE_SIZE
>>>> +
>>>> +/* The native architecture */
>>>> +#define KEXEC_ARCH KEXEC_ARCH_LOONGARCH
>>>> +
>>>> +static inline void crash_setup_regs(struct pt_regs *newregs,
>>>> +                    struct pt_regs *oldregs)
>>>> +{
>>>> +    if (oldregs)
>>>> +        memcpy(newregs, oldregs, sizeof(*newregs));
>>>> +    else
>>>> +        prepare_frametrace(newregs);
>>>> +}
>>>> +
>>>> +#define ARCH_HAS_KIMAGE_ARCH
>>>> +
>>>> +struct kimage_arch {
>>>> +    unsigned long boot_flag;
>>>> +    unsigned long fdt_addr;
>>>> +};
>>>> +
>>>> +typedef void (*do_kexec_t)(unsigned long boot_flag,
>>>> +               unsigned long fdt_addr,
>>>> +               unsigned long first_ind_entry,
>>>> +               unsigned long jump_addr);
>>>> +
>>>> +struct kimage;
>>>> +extern const unsigned char relocate_new_kernel[];
>>>> +extern const size_t relocate_new_kernel_size;
>>>> +
>>>> +#ifdef CONFIG_SMP
>>>> +extern atomic_t kexec_ready_to_reboot;
>>>> +extern const unsigned char kexec_smp_wait[];
>>>> +extern void kexec_reboot(void);
>>>> +#endif
>>>> +
>>>> +#endif /* !_ASM_KEXEC_H */
>>>> diff --git a/arch/loongarch/kernel/Makefile
>>>> b/arch/loongarch/kernel/Makefile
>>>> index a213e994db68..20b64ac3f128 100644
>>>> --- a/arch/loongarch/kernel/Makefile
>>>> +++ b/arch/loongarch/kernel/Makefile
>>>> @@ -17,6 +17,8 @@ obj-$(CONFIG_CPU_HAS_FPU)    += fpu.o
>>>>    obj-$(CONFIG_MODULES)        += module.o module-sections.o
>>>>    obj-$(CONFIG_STACKTRACE)    += stacktrace.o
>>>>    +obj-$(CONFIG_KEXEC)             += machine_kexec.o relocate_kernel.o
>>>> +
>>>>    obj-$(CONFIG_PROC_FS)        += proc.o
>>>>      obj-$(CONFIG_SMP)        += smp.o
>>>> diff --git a/arch/loongarch/kernel/head.S b/arch/loongarch/kernel/head.S
>>>> index 01bac62a6442..22bdf4928325 100644
>>>> --- a/arch/loongarch/kernel/head.S
>>>> +++ b/arch/loongarch/kernel/head.S
>>>> @@ -20,7 +20,12 @@
>>>>      _head:
>>>>        .word    MZ_MAGIC        /* "MZ", MS-DOS header */
>>>> -    .org    0x3c            /* 0x04 ~ 0x3b reserved */
>>>> +    .org    0x8
>>>> +    .quad    0            /* Image load offset from start of RAM */
>>>> +    .dword    _end - _text        /* Effective size of kernel image */
>>>> +    .quad    0
>>>> +    .dword    kernel_entry        /* Kernel entry point */
>>>> +    .org    0x3c            /* 0x28 ~ 0x3b reserved */
>>>>        .long    pe_header - _head    /* Offset to the PE header */
>>>>      pe_header:
>>>> diff --git a/arch/loongarch/kernel/machine_kexec.c
>>>> b/arch/loongarch/kernel/machine_kexec.c
>>>> new file mode 100644
>>>> index 000000000000..4ffcd4cd9c8c
>>>> --- /dev/null
>>>> +++ b/arch/loongarch/kernel/machine_kexec.c
>>>> @@ -0,0 +1,178 @@
>>>> +// SPDX-License-Identifier: GPL-2.0-only
>>>> +/*
>>>> + * machine_kexec.c for kexec
>>>> + *
>>>> + * Copyright (C) 2022 Loongson Technology Corporation Limited
>>>> + */
>>>> +#include <linux/compiler.h>
>>>> +#include <linux/cpu.h>
>>>> +#include <linux/kexec.h>
>>>> +#include <linux/mm.h>
>>>> +#include <linux/delay.h>
>>>> +#include <linux/libfdt.h>
>>>> +#include <linux/of_fdt.h>
>>>> +
>>>> +#include <asm/bootinfo.h>
>>>> +#include <asm/cacheflush.h>
>>>> +#include <asm/page.h>
>>>> +
>>>> +/* 0x100000 ~ 0x200000 is safe */
>>>> +#define KEXEC_CTRL_CODE    TO_CACHE(0x100000UL)
>>>> +#define KEXEC_BLOB_ADDR    TO_CACHE(0x108000UL)
>>>> +
>>>> +static unsigned long reboot_code_buffer;
>>>> +#ifdef CONFIG_SMP
>>>> +void (*relocated_kexec_smp_wait)(void *);
>>>> +atomic_t kexec_ready_to_reboot = ATOMIC_INIT(0);
>>>> +#endif
>>>> +
>>>> +static unsigned long jump_addr;
>>>> +static unsigned long first_ind_entry;
>>>> +static unsigned long boot_flag;
>>>> +static unsigned long fdt_addr;
>>>> +
>>>> +static void kexec_image_info(const struct kimage *kimage)
>>>> +{
>>>> +    unsigned long i;
>>>> +
>>>> +    pr_debug("kexec kimage info:\n");
>>>> +    pr_debug("\ttype:        %d\n", kimage->type);
>>>> +    pr_debug("\tstart:       %lx\n", kimage->start);
>>>> +    pr_debug("\thead:        %lx\n", kimage->head);
>>>> +    pr_debug("\tnr_segments: %lu\n", kimage->nr_segments);
>>>> +
>>>> +    for (i = 0; i < kimage->nr_segments; i++) {
>>>> +        pr_debug("\t    segment[%lu]: %016lx - %016lx", i,
>>>> +            kimage->segment[i].mem,
>>>> +            kimage->segment[i].mem + kimage->segment[i].memsz);
>>>> +        pr_debug("\t\t0x%lx bytes, %lu pages\n",
>>>> +            (unsigned long)kimage->segment[i].memsz,
>>>> +            (unsigned long)kimage->segment[i].memsz /  PAGE_SIZE);
>>>> +    }
>>>> +}
>>>> +
>>>> +int machine_kexec_prepare(struct kimage *kimage)
>>>> +{
>>>> +    int i;
>>>> +    void *dtb = (void *)KEXEC_BLOB_ADDR;
>>>> +
>>>> +    kexec_image_info(kimage);
>>>> +
>>>> +    /* Find the Flattened Device Tree */
>>>> +    for (i = 0; i < kimage->nr_segments; i++) {
>>>> +        if (!fdt_check_header(kimage->segment[i].buf)) {
>>>> +            memcpy(dtb, kimage->segment[i].buf, SZ_64K);
>>>> +            kimage->arch.boot_flag = fw_arg0;
>>>> +            kimage->arch.fdt_addr = (unsigned long) dtb;
>>>> +            break;
>>>> +        }
>>>> +        continue;
>>>> +    }
>>>> +
>>>> +    /* kexec need a safe page to save reboot_code_buffer */
>>>> +    kimage->control_code_page = virt_to_page((void *)KEXEC_CTRL_CODE);
>>>> +
>>>> +    reboot_code_buffer =
>>>> +      (unsigned long)page_address(kimage->control_code_page);
>>>> +    memcpy((void *)reboot_code_buffer, relocate_new_kernel,
>>>> +           relocate_new_kernel_size);
>>> It copys same content to KEXEC_CTRL_CODE each time, could we do this at
>>> boot time?
>> I think it's possible to have the copy action happen at boot-time or
>> during the prepare phase. (RISCV in prepare, MIPS in boot-time)
>>
>>> BTW, our system always keep the low-2MB no used, on mips-loongson or
>>> LoongArch. Is that necessary on LoongArch? We cannot use parameter
>>> 'mem=YYM' normally but 'mem=YYM@2M' is ok. And the low-2MB is not
>>> in virtual memory management, although we can get it in kernel.
>> For existing kernels, the low 2M has been reserved by
>> memblock_reserve(PHYS_OFFSET, 0x200000), maybe it is acceptable to keep
>> the low 2M behavior.
>>
>> Yes, we need to use "mem=YM@2M" if the low 2M is reserved.
>>
>>> In kexec/kdump process, we can follows kimage_alloc_control_pages().
>>> When the boot cpu copy complete the second-kernels, all cpus can jump
>>> to a kernel-entry-trampoline which is in kernel image. Then we don't
>>> worry about the code can be destroyed. The kernel-entry-trampoline
>>> get its cpuid, keep non-boot cpus do as kexec_smp_wait and let boot
>>> cpu go kernel-entry. In this way we can drop the low-2MB IMO.
>> It is also feasible to dynamically allocate control pages, but it is
>> easier to use a low 2M approach. What do you think, Huacai?
> I prefer to use the low 2MB.
>
> Huacai
Low 2MB also is ok for me, like a trick. And should it free
control_code_page here?

>>>> +
>>>> +    /* All secondary cpus now may jump to kexec_smp_wait cycle */
>>>> +    relocated_kexec_smp_wait = reboot_code_buffer +
>>>> +        (void *)(kexec_smp_wait - relocate_new_kernel);
>>>> +
>>>> +    return 0;
>>>> +}
>>>> +
>>>> +void machine_kexec_cleanup(struct kimage *kimage)
>>>> +{
>>>> +}
>>>> +
>>>> +#ifdef CONFIG_SMP
>>>> +void kexec_reboot(void)
>>>> +{
>>>> +    do_kexec_t do_kexec = NULL;
>>>> +
>>>> +    /* All secondary cpus go to kexec_smp_wait */
>>>> +    if (smp_processor_id() > 0) {
>>>> +        relocated_kexec_smp_wait(NULL);
>>>> +        unreachable();
>>>> +    }
>>>> +
>>>> +    do_kexec = (void *)reboot_code_buffer;
>>>> +    do_kexec(boot_flag, fdt_addr, first_ind_entry, jump_addr);
>>>> +
>>>> +    unreachable();
>>>> +}
>>>> +
>>>> +static void kexec_shutdown_secondary(void *)
>>>> +{
>>>> +    local_irq_disable();
>>>> +    while (!atomic_read(&kexec_ready_to_reboot))
>>>> +        cpu_relax();
>>>> +
>>>> +    kexec_reboot();
>>>> +}
>>>> +
>>>> +void machine_crash_shutdown(struct pt_regs *regs)
>>>> +{
>>>> +}
>>>> +#endif
>>>> +
>>>> +void machine_shutdown(void)
>>>> +{
>>>> +    smp_call_function(kexec_shutdown_secondary, NULL, 0);
>>>> +}
>>>> +
>>>> +void machine_kexec(struct kimage *image)
>>>> +{
>>>> +    unsigned long entry;
>>>> +    unsigned long *ptr;
>>>> +    struct kimage_arch *internal = &image->arch;
>>>> +
>>>> +    boot_flag = internal->boot_flag;
>>>> +    fdt_addr = internal->fdt_addr;
>>>> +
>>>> +    jump_addr = (unsigned long)phys_to_virt(image->start);
>>>> +
>>>> +    first_ind_entry = (unsigned long)phys_to_virt(image->head &
>>>> PAGE_MASK);
>>>> +
>>>> +    /*
>>>> +     * The generic kexec code builds a page list with physical
>>>> +     * addresses. they are directly accessible through XKPRANGE
>>>> +     * hence the phys_to_virt() call.
>>>> +     */
>>>> +    for (ptr = &image->head; (entry = *ptr) && !(entry & IND_DONE);
>>>> +         ptr = (entry & IND_INDIRECTION) ?
>>>> +           phys_to_virt(entry & PAGE_MASK) : ptr + 1) {
>>>> +        if (*ptr & IND_SOURCE || *ptr & IND_INDIRECTION ||
>>>> +            *ptr & IND_DESTINATION)
>>>> +            *ptr = (unsigned long) phys_to_virt(*ptr);
>>>> +    }
>>>> +
>>>> +    /* Mark offline before disabling local irq. */
>>>> +    set_cpu_online(smp_processor_id(), false);
>>>> +
>>>> +    /* we do not want to be bothered. */
>>>> +    local_irq_disable();
>>>> +
>>>> +    pr_notice("Will call new kernel at %lx\n", jump_addr);
>>>> +    pr_notice("FDT image at %lx\n", fdt_addr);
>>>> +    pr_notice("Bye ...\n");
>>>> +
>>>> +    /* Make reboot code buffer available to the boot CPU. */
>>>> +    flush_cache_all();
>>>> +
>>>> +    atomic_set(&kexec_ready_to_reboot, 1);
>>>> +
>>>> +    /*
>>>> +     * We know we were online, and there will be no incoming IPIs at
>>>> +     * this point.
>>>> +     */
>>>> +    set_cpu_online(smp_processor_id(), true);
>>>> +
>>>> +    /* Ensure remote CPUs observe that we're online before rebooting. */
>>>> +    smp_mb__after_atomic();
>>>> +
>>>> +    kexec_reboot();
>>>> +}
>>>> diff --git a/arch/loongarch/kernel/relocate_kernel.S
>>>> b/arch/loongarch/kernel/relocate_kernel.S
>>>> new file mode 100644
>>>> index 000000000000..d1f242f74ea8
>>>> --- /dev/null
>>>> +++ b/arch/loongarch/kernel/relocate_kernel.S
>>>> @@ -0,0 +1,125 @@
>>>> +/* SPDX-License-Identifier: GPL-2.0 */
>>>> +/*
>>>> + * relocate_kernel.S for kexec
>>>> + *
>>>> + * Copyright (C) 2022 Loongson Technology Corporation Limited
>>>> + */
>>>> +
>>>> +#include <linux/kexec.h>
>>>> +
>>>> +#include <asm/asm.h>
>>>> +#include <asm/asmmacro.h>
>>>> +#include <asm/regdef.h>
>>>> +#include <asm/loongarch.h>
>>>> +#include <asm/stackframe.h>
>>>> +#include <asm/addrspace.h>
>>>> +
>>>> +#define IPI_REG_BASE 0x1fe01000
>>>> +
>>>> +SYM_CODE_START(relocate_new_kernel)
>>>> +    /*
>>>> +     * s0: Boot flag passed to the new kernel
>>>> +     * s1: Virt address of the FDT image
>>>> +     * s2: Pointer to the current entry
>>>> +     * s3: Virt address to jump to after relocation
>>>> +     */
>>>> +    move        s0, a0
>>>> +    move        s1, a1
>>>> +    move        s2, a2
>>>> +    move        s3, a3
>>>> +
>>>> +process_entry:
>>>> +    PTR_L        s4, s2, 0
>>>> +    PTR_ADDI    s2, s2, SZREG
>>>> +
>>>> +    /* destination page */
>>>> +    andi        s5, s4, IND_DESTINATION
>>>> +    beqz        s5, 1f
>>>> +    li.w        t0, ~0x1
>>>> +    and        s6, s4, t0    /* store destination addr in s6 */
>>>> +    b        process_entry
>>>> +
>>>> +1:
>>>> +    /* indirection page, update s2    */
>>>> +    andi        s5, s4, IND_INDIRECTION
>>>> +    beqz        s5, 1f
>>>> +    li.w        t0, ~0x2
>>>> +    and        s2, s4, t0
>>>> +    b        process_entry
>>>> +
>>>> +1:
>>>> +    /* done page */
>>>> +    andi        s5, s4, IND_DONE
>>>> +    beqz        s5, 1f
>>>> +    b        done
>>>> +1:
>>>> +    /* source page */
>>>> +    andi        s5, s4, IND_SOURCE
>>>> +    beqz        s5, process_entry
>>>> +    li.w        t0, ~0x8
>>>> +    and        s4, s4, t0
>>>> +    li.w        s8, (1 << _PAGE_SHIFT) / SZREG
>>>> +
>>>> +copy_word:
>>>> +    /* copy page word by word */
>>>> +    REG_L        s7, s4, 0
>>>> +    REG_S        s7, s6, 0
>>>> +    PTR_ADDI    s6, s6, SZREG
>>>> +    PTR_ADDI    s4, s4, SZREG
>>>> +    LONG_ADDI    s8, s8, -1
>>>> +    beqz        s8, process_entry
>>>> +    b        copy_word
>>>> +    b        process_entry
>>>> +
>>>> +done:
>>>> +    dbar        0
>>> ibar, too?
>> Will add ibar 0.
>>
>>>> +
>>>> +    move        a0, s0
>>>> +    move        a1, s1
>>>> +    /* jump to the new kernel */
>>>> +    jr        s3
>>>> +SYM_CODE_END(relocate_new_kernel)
>>>> +
>>>> +#ifdef CONFIG_SMP
>>>> +/*
>>>> + * Other CPUs should wait until code is relocated and
>>>> + * then start at entry (?) point.
>>>> + */
>>>> +SYM_CODE_START(kexec_smp_wait)
>>>> +    li.d        t0, IPI_REG_BASE
>>>> +    li.d        t1, UNCACHE_BASE
>>>> +    or        t0, t0, t1
>>>> +
>>>> +    /*
>>>> +     * s1:initfn
>>>> +     * t0:base t1:cpuid t2:node t3:core t4:count
>>>> +     */
>>>> +    csrrd        t1, LOONGARCH_CSR_CPUID
>>>> +    andi        t1, t1, CSR_CPUID_COREID
>>>> +    andi        t3, t1, 0x3
>>>> +    slli.w        t3, t3, 8              /* get core id */
>>>> +    or        t0, t0, t3
>>>> +    andi        t2, t1, 0x3c
>>>> +    slli.d        t2, t2, 42             /* get node id */
>>>> +    or        t0, t0, t2
>>>> +
>>>> +1:    li.w        t4, 0x100              /* wait for init loop */
>>>> +2:    addi.w        t4, t4, -1             /* limit mailbox access */
>>>> +    bnez        t4, 2b
>>>> +    ld.w        s1, t0, 0x20           /* check PC as an indicator */
>>> Can we do this with iocsr*?
>> OK, I will consider the implementation in the iocsr way.
>>
>> Thanks,
>> Youling
>>> Thanks,
>>> Jinyang
>>>> +    beqz        s1, 1b
>>>> +    ld.d        s1, t0, 0x20           /* get PC via mailbox */
>>>> +    ld.d        sp, t0, 0x28           /* get SP via mailbox */
>>>> +    ld.d        tp, t0, 0x30           /* get TP via mailbox */
>>>> +
>>>> +    li.d        t0, CACHE_BASE
>>>> +    or        s1, s1, t0
>>>> +    jr        s1                     /* jump to initial PC */
>>>> +SYM_CODE_END(kexec_smp_wait)
>>>> +#endif
>>>> +
>>>> +relocate_new_kernel_end:
>>>> +
>>>> +SYM_DATA_START(relocate_new_kernel_size)
>>>> +    PTR        relocate_new_kernel_end - relocate_new_kernel
>>>> +SYM_DATA_END(relocate_new_kernel_size)

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