[Xen-devel] [PATCH] x86: avoid redundant TLB flushes

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

While in some places the guest requested flushes were already folded
into the deferred ops, this wasn't done consistently.

Also avoid using an uninitialized variable, even if doing so has no
correctness issue.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

--- 2009-01-30.orig/xen/arch/x86/mm.c   2009-01-30 10:13:53.000000000 +0100
+++ 2009-01-30/xen/arch/x86/mm.c        2009-02-03 13:54:43.000000000 +0100
@@ -2773,7 +2773,7 @@ int do_mmuext_op(
         }
 
         case MMUEXT_TLB_FLUSH_ALL:
-            flush_tlb_mask(d->domain_dirty_cpumask);
+            this_cpu(percpu_mm_info).deferred_ops |= DOP_FLUSH_ALL_TLBS;
             break;
     
         case MMUEXT_INVLPG_ALL:
@@ -3567,34 +3567,40 @@ int do_update_va_mapping(unsigned long v
     if ( pl1e )
         guest_unmap_l1e(v, pl1e);
 
-    process_deferred_ops();
-
     switch ( flags & UVMF_FLUSHTYPE_MASK )
     {
     case UVMF_TLB_FLUSH:
         switch ( (bmap_ptr = flags & ~UVMF_FLUSHTYPE_MASK) )
         {
         case UVMF_LOCAL:
-            flush_tlb_local();
+            this_cpu(percpu_mm_info).deferred_ops |= DOP_FLUSH_TLB;
             break;
         case UVMF_ALL:
-            flush_tlb_mask(d->domain_dirty_cpumask);
+            this_cpu(percpu_mm_info).deferred_ops |= DOP_FLUSH_ALL_TLBS;
             break;
         default:
+            if ( this_cpu(percpu_mm_info).deferred_ops & DOP_FLUSH_ALL_TLBS )
+                break;
             if ( unlikely(!is_pv_32on64_domain(d) ?
                           get_user(vmask, (unsigned long *)bmap_ptr) :
                           get_user(vmask, (unsigned int *)bmap_ptr)) )
-                rc = -EFAULT;
+                rc = -EFAULT, vmask = 0;
             pmask = vcpumask_to_pcpumask(d, vmask);
+            if ( cpu_isset(smp_processor_id(), pmask) )
+                this_cpu(percpu_mm_info).deferred_ops &= ~DOP_FLUSH_TLB;
             flush_tlb_mask(pmask);
             break;
         }
         break;
 
     case UVMF_INVLPG:
+        if ( this_cpu(percpu_mm_info).deferred_ops & DOP_FLUSH_ALL_TLBS )
+            break;
         switch ( (bmap_ptr = flags & ~UVMF_FLUSHTYPE_MASK) )
         {
         case UVMF_LOCAL:
+            if ( this_cpu(percpu_mm_info).deferred_ops & DOP_FLUSH_TLB )
+                break;
             if ( !paging_mode_enabled(d) ||
                  (paging_invlpg(v, va) != 0) ) 
                 flush_tlb_one_local(va);
@@ -3606,14 +3612,18 @@ int do_update_va_mapping(unsigned long v
             if ( unlikely(!is_pv_32on64_domain(d) ?
                           get_user(vmask, (unsigned long *)bmap_ptr) :
                           get_user(vmask, (unsigned int *)bmap_ptr)) )
-                rc = -EFAULT;
+                rc = -EFAULT, vmask = 0;
             pmask = vcpumask_to_pcpumask(d, vmask);
+            if ( this_cpu(percpu_mm_info).deferred_ops & DOP_FLUSH_TLB )
+                cpu_clear(smp_processor_id(), pmask);
             flush_tlb_one_mask(pmask, va);
             break;
         }
         break;
     }
 
+    process_deferred_ops();
+
     return rc;
 }
 




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