From: George Dunlap <dunlapg@umich.edu>
Date: Tue, 16 Jan 2007 19:04:12 +0000 (-0500)
Subject: [XEN] Fix early-unshadow detection for 3- or 4-level guest pagetables.
X-Git-Tag: archive/raspbian/4.8.0-1+rpi1~1^2~15396^2~14
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=a086d29d0e360e83eafed55959c3e4e2a1340a38;p=xen.git

[XEN] Fix early-unshadow detection for 3- or 4-level guest pagetables.
Early-unshadow will unshadow whenever 2 zero values are written
to the same page; for PAE, one PTE takes 2 writes.  Only check
for the early unshadow when writing the low half of the PTE.
---

diff --git a/xen/arch/x86/mm/shadow/multi.c b/xen/arch/x86/mm/shadow/multi.c
index e040e60e71..0546cb1a66 100644
--- a/xen/arch/x86/mm/shadow/multi.c
+++ b/xen/arch/x86/mm/shadow/multi.c
@@ -3944,7 +3944,7 @@ sh_x86_emulate_write(struct vcpu *v, unsigned long vaddr, void *src,
     if ( !skip ) sh_validate_guest_pt_write(v, mfn, addr, bytes);
 
     /* If we are writing zeros to this page, might want to unshadow */
-    if ( likely(bytes >= 4) && (*(u32 *)addr == 0) )
+    if ( likely(bytes >= 4) && (*(u32 *)addr == 0) && is_lo_pte(vaddr) )
         check_for_early_unshadow(v, mfn);
 
     sh_unmap_domain_page(addr);
@@ -3996,7 +3996,7 @@ sh_x86_emulate_cmpxchg(struct vcpu *v, unsigned long vaddr,
                   vaddr, prev, old, new, *(unsigned long *)addr, bytes);
 
     /* If we are writing zeros to this page, might want to unshadow */
-    if ( likely(bytes >= 4) && (*(u32 *)addr == 0) )
+    if ( likely(bytes >= 4) && (*(u32 *)addr == 0) && is_lo_pte(vaddr) )
         check_for_early_unshadow(v, mfn);
 
     sh_unmap_domain_page(addr);
diff --git a/xen/arch/x86/mm/shadow/private.h b/xen/arch/x86/mm/shadow/private.h
index 913fa43770..21d78eb2de 100644
--- a/xen/arch/x86/mm/shadow/private.h
+++ b/xen/arch/x86/mm/shadow/private.h
@@ -427,6 +427,11 @@ extern int sh_remove_write_access(struct vcpu *v, mfn_t readonly_mfn,
 #undef mfn_valid
 #define mfn_valid(_mfn) (mfn_x(_mfn) < max_page)
 
+#if GUEST_PAGING_LEVELS >= 3
+# define is_lo_pte(_vaddr) (((_vaddr)&0x4)==0)
+#else
+# define is_lo_pte(_vaddr) (1)
+#endif
 
 static inline int
 sh_mfn_is_a_page_table(mfn_t gmfn)