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[PATCH 0/3] x86/mm: Straightforward TLB flush fixes/cleanups

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  [PATCH 0/3] x86/mm: Straightforward TLB flush fixes/cleanups Andy Lutomirski <luto@kernel.org> - 2017-04-21 20:30 +0200
    [PATCH 2/3] x86/mm: Make flush_tlb_mm_range() more predictable Andy Lutomirski <luto@kernel.org> - 2017-04-21 20:30 +0200

#1628428 — [PATCH 0/3] x86/mm: Straightforward TLB flush fixes/cleanups

I have some less straightforward cleanups coming, but these three
are easy and might even be okay for 4.12 assuming that someone feels
like reviewing them.

Andy Lutomirski (3):
  x86/mm: Remove flush_tlb() and flush_tlb_current_task()
  x86/mm: Make flush_tlb_mm_range() more predictable
  x86/mm: Fix flush_tlb_page() on Xen

 arch/x86/include/asm/tlbflush.h |  3 ---
 arch/x86/mm/tlb.c               | 33 ++++++++-------------------------
 2 files changed, 8 insertions(+), 28 deletions(-)

-- 
2.9.3

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#1628430 — [PATCH 2/3] x86/mm: Make flush_tlb_mm_range() more predictable

I'm about to rewrite the function almost completely, but first I
want to get a functional change out of the way.  Currently, if
flush_tlb_mm_range() does not flush the local TLB at all, it will
never do individual page flushes on remote CPUs.  This seems to be
an accident, and preserving it will be awkward.  Let's change it
first so that any regressions in the rewrite will be easier to
bisect and so that the rewrite can attempt to change no visible
behavior at all.

The fix is simple: we can simply avoid short-circuiting the
calculation of base_pages_to_flush.

As a side effect, this also eliminates a potential corner case: if
tlb_single_page_flush_ceiling == TLB_FLUSH_ALL, flush_tlb_mm_range()
could have ended up flushing the entire address space one page at a
time.

Cc: Rik van Riel <riel@redhat.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/mm/tlb.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 92ec37f517ab..9db9260a5e9f 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -309,6 +309,12 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
 	unsigned long base_pages_to_flush = TLB_FLUSH_ALL;
 
 	preempt_disable();
+
+	if ((end != TLB_FLUSH_ALL) && !(vmflag & VM_HUGETLB))
+		base_pages_to_flush = (end - start) >> PAGE_SHIFT;
+	if (base_pages_to_flush > tlb_single_page_flush_ceiling)
+		base_pages_to_flush = TLB_FLUSH_ALL;
+
 	if (current->active_mm != mm) {
 		/* Synchronize with switch_mm. */
 		smp_mb();
@@ -325,15 +331,11 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
 		goto out;
 	}
 
-	if ((end != TLB_FLUSH_ALL) && !(vmflag & VM_HUGETLB))
-		base_pages_to_flush = (end - start) >> PAGE_SHIFT;
-
 	/*
 	 * Both branches below are implicit full barriers (MOV to CR or
 	 * INVLPG) that synchronize with switch_mm.
 	 */
-	if (base_pages_to_flush > tlb_single_page_flush_ceiling) {
-		base_pages_to_flush = TLB_FLUSH_ALL;
+	if (base_pages_to_flush == TLB_FLUSH_ALL) {
 		count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL);
 		local_flush_tlb();
 	} else {
-- 
2.9.3

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