x86/mm: Give each mm TLB flush generation a unique ID

This adds two new variables to mmu_context_t: ctx_id and tlb_gen.
ctx_id uniquely identifies the mm_struct and will never be reused.
For a given mm_struct (and hence ctx_id), tlb_gen is a monotonic
count of the number of times that a TLB flush has been requested.
The pair (ctx_id, tlb_gen) can be used as an identifier for TLB
flush actions and will be used in subsequent patches to reliably
determine whether all needed TLB flushes have occurred on a given
CPU.

This patch is split out for ease of review.  By itself, it has no
real effect other than creating and updating the new variables.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Nadav Amit <nadav.amit@gmail.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/413a91c24dab3ed0caa5f4e4d017d87b0857f920.1498751203.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 18 insertions, 0 deletions

diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 50ea3482e1d1..ad2135385699 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -57,6 +57,23 @@ static inline void invpcid_flush_all_nonglobals(void)
 	__invpcid(0, 0, INVPCID_TYPE_ALL_NON_GLOBAL);
 }
 
+static inline u64 inc_mm_tlb_gen(struct mm_struct *mm)
+{
+	u64 new_tlb_gen;
+
+	/*
+	 * Bump the generation count.  This also serves as a full barrier
+	 * that synchronizes with switch_mm(): callers are required to order
+	 * their read of mm_cpumask after their writes to the paging
+	 * structures.
+	 */
+	smp_mb__before_atomic();
+	new_tlb_gen = atomic64_inc_return(&mm->context.tlb_gen);
+	smp_mb__after_atomic();
+
+	return new_tlb_gen;
+}
+
 #ifdef CONFIG_PARAVIRT
 #include <asm/paravirt.h>
 #else
@@ -262,6 +279,7 @@ void native_flush_tlb_others(const struct cpumask *cpumask,
 static inline void arch_tlbbatch_add_mm(struct arch_tlbflush_unmap_batch *batch,
 					struct mm_struct *mm)
 {
+	inc_mm_tlb_gen(mm);
 	cpumask_or(&batch->cpumask, &batch->cpumask, mm_cpumask(mm));
 }