[Xen-devel] [PATCH] Fix OOS typecounting [was: Test report for Xen-3.3.0-rc4 (#18314)]

[Gianluca Guida <gianluca.guida@xxxxxxxxxxxxx>]

Hello,

Keir Fraser wrote:

> We still need to decide whether to fix the second issue or disable OOS.
The attached patch should fix this issue. It was an all-my-fault 
breakage of set_l1e atomicity.
> We're not decided on that just yet. If it reproed more reliably for us then
> I'd be more optimistic about fixing it. Perhaps I will switch to 32pae as so
> far I've been running 32e host.
A very easy way to reproduce this bug is to set SHADOW_OOS_FIXUPS to 1 
in xen/include/asm-x86/mm.h. This will reproduce very quickly the 
typecount corruption.
Gianluca

diff -r d3947223dfae xen/arch/x86/mm/shadow/multi.c
--- a/xen/arch/x86/mm/shadow/multi.c    Thu Aug 14 13:46:48 2008 +0100
+++ b/xen/arch/x86/mm/shadow/multi.c    Thu Aug 14 10:31:12 2008 -0400
@@ -1415,6 +1415,15 @@ static int shadow_set_l1e(struct vcpu *v
     mfn_t new_gmfn = shadow_l1e_get_mfn(new_sl1e);
 #endif
     ASSERT(sl1e != NULL);
+
+#if SHADOW_OPTIMIZATIONS & SHOPT_OUT_OF_SYNC
+    if ( mfn_valid(new_gmfn) && mfn_oos_may_write(new_gmfn)
+         && ((shadow_l1e_get_flags(new_sl1e) & (_PAGE_RW|_PAGE_PRESENT))
+             == (_PAGE_RW|_PAGE_PRESENT)) )
+    {
+        oos_fixup_add(v, new_gmfn, sl1mfn, pgentry_ptr_to_slot(sl1e));
+    }
+#endif
     
     old_sl1e = *sl1e;
 
@@ -1434,14 +1443,6 @@ static int shadow_set_l1e(struct vcpu *v
             else
             {
                 shadow_vram_get_l1e(new_sl1e, sl1e, sl1mfn, d);
-#if SHADOW_OPTIMIZATIONS & SHOPT_OUT_OF_SYNC
-                if ( mfn_valid(new_gmfn) && mfn_oos_may_write(new_gmfn)
-                     && (shadow_l1e_get_flags(new_sl1e) & _PAGE_RW) )
-                {
-                    oos_fixup_add(v, new_gmfn, sl1mfn, 
pgentry_ptr_to_slot(sl1e));
-                }
-#endif
-
             }
         }
     } 

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