From: tip-bot for Andy Lutomirski <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: hpa@zytor.com, riel@redhat.com, luto@kernel.org,
tglx@linutronix.de, luto@amacapital.net, dvlasenk@redhat.com,
linux-kernel@vger.kernel.org, peterz@infradead.org,
torvalds@linux-foundation.org, mingo@kernel.org, bp@alien8.de,
brgerst@gmail.com, dave.hansen@linux.intel.com
Subject: [tip:x86/urgent] x86/mm: Improve switch_mm() barrier comments
Date: Thu, 14 Jan 2016 01:06:43 -0800 [thread overview]
Message-ID: <tip-4eaffdd5a5fe6ff9f95e1ab4de1ac904d5e0fa8b@git.kernel.org> (raw)
In-Reply-To: <0a0b43cdcdd241c5faaaecfbcc91a155ddedc9a1.1452631609.git.luto@kernel.org>
Commit-ID: 4eaffdd5a5fe6ff9f95e1ab4de1ac904d5e0fa8b
Gitweb: http://git.kernel.org/tip/4eaffdd5a5fe6ff9f95e1ab4de1ac904d5e0fa8b
Author: Andy Lutomirski <luto@kernel.org>
AuthorDate: Tue, 12 Jan 2016 12:47:40 -0800
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 13 Jan 2016 10:42:49 +0100
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>
---
arch/x86/include/asm/mmu_context.h | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)
diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index 1edc9cd..bfd9b2a 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);
prev parent reply other threads:[~2016-01-14 9:09 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <tip-71b3c126e61177eb693423f2e18a1914205b165e@git.kernel.org>
2016-01-11 18:25 ` [tip:x86/urgent] x86/mm: Add barriers and document switch_mm() -vs-flush synchronization Peter Zijlstra
2016-01-11 21:50 ` Andy Lutomirski
2016-01-11 22:22 ` Peter Zijlstra
2016-01-12 10:21 ` Ingo Molnar
2016-01-12 20:11 ` [PATCH] x86/mm: Improve switch_mm barrier comments Andy Lutomirski
2016-01-12 20:47 ` [PATCH v2] " Andy Lutomirski
2016-01-14 9:06 ` tip-bot for Andy Lutomirski [this message]
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