[Xen-changelog] [xen stable-4.6] x86: don't flush the whole cache when changing cachability

[patchbot@xxxxxxx]

commit 301d68384249382b6d0b4e49ee318d2903ec98cc
Author:     David Vrabel <david.vrabel@xxxxxxxxxx>
AuthorDate: Fri Mar 18 08:05:49 2016 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Mar 18 08:05:49 2016 +0100

    x86: don't flush the whole cache when changing cachability
    
    Introduce the FLUSH_VA_VALID flag to flush_area_mask() and friends to
    say that it is safe to use CLFLUSH (i.e., the virtual address is still
    valid).
    
    Use this when changing the cachability of the Xen direct mappings (in
    response to the guest changing the cachability of its mappings). This
    significantly improves performance by avoiding an expensive WBINVD.
    
    This fixes a performance regression introduced by
    c61a6f74f80eb36ed83a82f713db3143159b9009 (x86: enforce consistent
    cachability of MMIO mappings), the fix for XSA-154.
    
    e.g., A set_memory_wc() call in Linux:
    
    before: 4097 us
    after:    47 us
    
    Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: dff593c7b6eb1cfd4591b662a880a0c9325cce40
    master date: 2016-03-10 16:51:03 +0100
---
 xen/arch/x86/flushtlb.c        | 3 ++-
 xen/arch/x86/mm.c              | 5 +++++
 xen/include/asm-x86/flushtlb.h | 2 ++
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/flushtlb.c b/xen/arch/x86/flushtlb.c
index 5d5d79c..e2a5524 100644
--- a/xen/arch/x86/flushtlb.c
+++ b/xen/arch/x86/flushtlb.c
@@ -135,7 +135,8 @@ void flush_area_local(const void *va, unsigned int flags)
         if ( order < (BITS_PER_LONG - PAGE_SHIFT) )
             sz = 1UL << (order + PAGE_SHIFT);
 
-        if ( !(flags & (FLUSH_TLB|FLUSH_TLB_GLOBAL)) &&
+        if ( (!(flags & (FLUSH_TLB|FLUSH_TLB_GLOBAL)) ||
+              (flags & FLUSH_VA_VALID)) &&
              c->x86_clflush_size && c->x86_cache_size && sz &&
              ((sz >> 10) < c->x86_cache_size) )
         {
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 738b761..eed1efd 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -5557,7 +5557,12 @@ int map_pages_to_xen(
         flush_flags |= FLUSH_TLB_GLOBAL;       \
     if ( (flags & _PAGE_PRESENT) &&            \
          (((o_) ^ flags) & PAGE_CACHE_ATTRS) ) \
+    {                                          \
         flush_flags |= FLUSH_CACHE;            \
+        if ( virt >= DIRECTMAP_VIRT_START &&   \
+             virt < HYPERVISOR_VIRT_END )      \
+            flush_flags |= FLUSH_VA_VALID;     \
+    }                                          \
 } while (0)
 
     while ( nr_mfns != 0 )
diff --git a/xen/include/asm-x86/flushtlb.h b/xen/include/asm-x86/flushtlb.h
index 8dbe2d6..3c3e6b2 100644
--- a/xen/include/asm-x86/flushtlb.h
+++ b/xen/include/asm-x86/flushtlb.h
@@ -85,6 +85,8 @@ void write_cr3(unsigned long cr3);
 #define FLUSH_TLB_GLOBAL 0x200
  /* Flush data caches */
 #define FLUSH_CACHE      0x400
+ /* VA for the flush has a valid mapping */
+#define FLUSH_VA_VALID   0x800
 
 /* Flush local TLBs/caches. */
 void flush_area_local(const void *va, unsigned int flags);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.6

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