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Date: Wed, 17 Jan 2018 11:54:56 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
Andy Lutomirski <luto@...nel.org>,
"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
Boqun Feng <boqun.feng@...il.com>,
Andrew Hunter <ahh@...gle.com>,
Maged Michael <maged.michael@...il.com>,
Avi Kivity <avi@...lladb.com>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>,
Michael Ellerman <mpe@...erman.id.au>,
Dave Watson <davejwatson@...com>,
"H . Peter Anvin" <hpa@...or.com>,
Andrea Parri <parri.andrea@...il.com>,
Russell King <linux@...linux.org.uk>,
Greg Hackmann <ghackmann@...gle.com>,
Will Deacon <will.deacon@....com>,
David Sehr <sehr@...gle.com>,
Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
linux-arch@...r.kernel.org
Subject: [PATCH for 4.16 09/11] membarrier: x86: Provide core serializing command (v4)
There are two places where core serialization is needed by membarrier:
1) When returning from the membarrier IPI,
2) After scheduler updates curr to a thread with a different mm, before
going back to user-space, since the curr->mm is used by membarrier to
check whether it needs to send an IPI to that CPU.
x86-32 uses iret as return from interrupt, and both iret and sysexit to go
back to user-space. The iret instruction is core serializing, but not
sysexit.
x86-64 uses iret as return from interrupt, which takes care of the IPI.
However, it can return to user-space through either sysretl (compat
code), sysretq, or iret. Given that sysret{l,q} is not core serializing,
we rely instead on write_cr3() performed by switch_mm() to provide core
serialization after changing the current mm, and deal with the special
case of kthread -> uthread (temporarily keeping current mm into
active_mm) by adding a sync_core() in that specific case.
Use the new sync_core_before_usermode() to guarantee this.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
CC: Peter Zijlstra <peterz@...radead.org>
CC: Andy Lutomirski <luto@...nel.org>
CC: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
CC: Boqun Feng <boqun.feng@...il.com>
CC: Andrew Hunter <ahh@...gle.com>
CC: Maged Michael <maged.michael@...il.com>
CC: Avi Kivity <avi@...lladb.com>
CC: Benjamin Herrenschmidt <benh@...nel.crashing.org>
CC: Paul Mackerras <paulus@...ba.org>
CC: Michael Ellerman <mpe@...erman.id.au>
CC: Dave Watson <davejwatson@...com>
CC: Thomas Gleixner <tglx@...utronix.de>
CC: Ingo Molnar <mingo@...hat.com>
CC: "H. Peter Anvin" <hpa@...or.com>
CC: Andrea Parri <parri.andrea@...il.com>
CC: Russell King <linux@...linux.org.uk>
CC: Greg Hackmann <ghackmann@...gle.com>
CC: Will Deacon <will.deacon@....com>
CC: David Sehr <sehr@...gle.com>
CC: x86@...nel.org
CC: linux-arch@...r.kernel.org
---
Changes since v1:
- Use the newly introduced sync_core_before_usermode(). Move all state
handling to generic code.
- Add linux/processor.h include to include/linux/sched/mm.h.
Changes since v2:
- Fix use-after-free in membarrier_mm_sync_core_before_usermode.
Changes since v3:
- Move generic code into separate patch.
---
arch/x86/Kconfig | 1 +
arch/x86/entry/entry_32.S | 5 +++++
arch/x86/entry/entry_64.S | 4 ++++
arch/x86/mm/tlb.c | 7 ++++---
4 files changed, 14 insertions(+), 3 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 0b44c8dd0e95..b5324f2e3162 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -54,6 +54,7 @@ config X86
select ARCH_HAS_FORTIFY_SOURCE
select ARCH_HAS_GCOV_PROFILE_ALL
select ARCH_HAS_KCOV if X86_64
+ select ARCH_HAS_MEMBARRIER_SYNC_CORE
select ARCH_HAS_PMEM_API if X86_64
select ARCH_HAS_REFCOUNT
select ARCH_HAS_UACCESS_FLUSHCACHE if X86_64
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index a1f28a54f23a..0c89cef690cf 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -554,6 +554,11 @@ restore_all:
.Lrestore_nocheck:
RESTORE_REGS 4 # skip orig_eax/error_code
.Lirq_return:
+ /*
+ * ARCH_HAS_MEMBARRIER_SYNC_CORE rely on iret core serialization
+ * when returning from IPI handler and when returning from
+ * scheduler to user-space.
+ */
INTERRUPT_RETURN
.section .fixup, "ax"
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 4f8e1d35a97c..8a32390240f1 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -792,6 +792,10 @@ GLOBAL(restore_regs_and_return_to_kernel)
POP_EXTRA_REGS
POP_C_REGS
addq $8, %rsp /* skip regs->orig_ax */
+ /*
+ * ARCH_HAS_MEMBARRIER_SYNC_CORE rely on iret core serialization
+ * when returning from IPI handler.
+ */
INTERRUPT_RETURN
ENTRY(native_iret)
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index c28cd5592b0d..df4e21371c89 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -201,9 +201,10 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
this_cpu_write(cpu_tlbstate.is_lazy, false);
/*
- * The membarrier system call requires a full memory barrier
- * before returning to user-space, after storing to rq->curr.
- * Writing to CR3 provides that full memory barrier.
+ * The membarrier system call requires a full memory barrier and
+ * core serialization before returning to user-space, after
+ * storing to rq->curr. Writing to CR3 provides that full
+ * memory barrier and core serializing instruction.
*/
if (real_prev == next) {
VM_WARN_ON(this_cpu_read(cpu_tlbstate.ctxs[prev_asid].ctx_id) !=
--
2.11.0
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