[Xen-changelog] Avoid some unnecessary TLB flushes. This will probably make no real

[Xen patchbot -unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User sos22@xxxxxxxxxxxxxxxxxxxx
# Node ID ebfde26a769a123dcb3b19ab03881a02ee2404fc
# Parent  e8b48f3a2843e79680147926fbe4ba94cce68589

Avoid some unnecessary TLB flushes.  This will probably make no real
difference on any sensible guest operating system.

Signed-off-by: Steven Smith, sos22@xxxxxxxxxxxxx

diff -r e8b48f3a2843 -r ebfde26a769a xen/arch/x86/mm.c
--- a/xen/arch/x86/mm.c Fri Jul 15 09:09:57 2005
+++ b/xen/arch/x86/mm.c Fri Jul 15 09:24:29 2005
@@ -1352,18 +1352,22 @@
         {
             if ( (x & (PGT_type_mask|PGT_va_mask)) != type )
             {
-                /*
-                 * On type change we check to flush stale TLB entries. This 
-                 * may be unnecessary (e.g., page was GDT/LDT) but those
-                 * circumstances should be very rare.
-                 */
-                cpumask_t mask = page_get_owner(page)->cpumask;
-                tlbflush_filter(mask, page->tlbflush_timestamp);
-
-                if ( unlikely(!cpus_empty(mask)) )
+                if ( (x & PGT_type_mask) != (type & PGT_type_mask) )
                 {
-                    perfc_incrc(need_flush_tlb_flush);
-                    flush_tlb_mask(mask);
+                    /*
+                     * On type change we check to flush stale TLB
+                     * entries. This may be unnecessary (e.g., page
+                     * was GDT/LDT) but those circumstances should be
+                     * very rare.
+                     */
+                    cpumask_t mask = page_get_owner(page)->cpumask;
+                    tlbflush_filter(mask, page->tlbflush_timestamp);
+
+                    if ( unlikely(!cpus_empty(mask)) )
+                    {
+                        perfc_incrc(need_flush_tlb_flush);
+                        flush_tlb_mask(mask);
+                    }
                 }
 
                 /* We lose existing type, back pointer, and validity. */

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