diff options
| author | Andy Lutomirski <luto@kernel.org> | 2016-01-12 12:47:40 -0800 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2016-01-13 10:42:49 +0100 |
| commit | 4eaffdd5a5fe6ff9f95e1ab4de1ac904d5e0fa8b (patch) | |
| tree | 81737b8f921080f0a4a5860bda80877c14772beb /arch/x86 | |
| parent | 65cacec1ba908a153cfb19c4de596a108f95970c (diff) | |
x86/mm: Improve switch_mm() barrier comments
My previous comments were still a bit confusing and there was a
typo. Fix it up.
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Fixes: 71b3c126e611 ("x86/mm: Add barriers and document switch_mm()-vs-flush synchronization")
Link: http://lkml.kernel.org/r/0a0b43cdcdd241c5faaaecfbcc91a155ddedc9a1.1452631609.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86')
| -rw-r--r-- | arch/x86/include/asm/mmu_context.h | 15 |
1 files changed, 8 insertions, 7 deletions
diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h index 1edc9cd198b8..bfd9b2a35a0b 100644 --- a/arch/x86/include/asm/mmu_context.h +++ b/arch/x86/include/asm/mmu_context.h @@ -132,14 +132,16 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, * be sent, and CPU 0's TLB will contain a stale entry.) * * The bad outcome can occur if either CPU's load is - * reordered before that CPU's store, so both CPUs much + * reordered before that CPU's store, so both CPUs must * execute full barriers to prevent this from happening. * * Thus, switch_mm needs a full barrier between the * store to mm_cpumask and any operation that could load - * from next->pgd. This barrier synchronizes with - * remote TLB flushers. Fortunately, load_cr3 is - * serializing and thus acts as a full barrier. + * from next->pgd. TLB fills are special and can happen + * due to instruction fetches or for no reason at all, + * and neither LOCK nor MFENCE orders them. + * Fortunately, load_cr3() is serializing and gives the + * ordering guarantee we need. * */ load_cr3(next->pgd); @@ -188,9 +190,8 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, * tlb flush IPI delivery. We must reload CR3 * to make sure to use no freed page tables. * - * As above, this is a barrier that forces - * TLB repopulation to be ordered after the - * store to mm_cpumask. + * As above, load_cr3() is serializing and orders TLB + * fills with respect to the mm_cpumask write. */ load_cr3(next->pgd); trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL); |