This should fix the host crash reported in the thread "d273:v3: 
reserved bit in page table (ec=0019)" (but it specifically doesn't deal
with the yet unknown original cause of the problem).
Also add in a missing line in x86-64's do_page_walk().
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
--- 2009年07月10日.orig/xen/arch/x86/x86_32/traps.c 2009年07月10日 13:58:56.000000000 
+0200
+++ 2009年07月10日/xen/arch/x86/x86_32/traps.c 2009年07月17日 11:12:42.000000000 
+0200
@@ -165,7 +165,8 @@ void show_page_walk(unsigned long addr)
 printk(" L3[0x%03lx] = %"PRIpte" %08lx\n",
 l3_table_offset(addr), l3e_get_intpte(l3e), pfn);
 unmap_domain_page(l3t);
- if ( !(l3e_get_flags(l3e) & _PAGE_PRESENT) )
+ if ( !(l3e_get_flags(l3e) & _PAGE_PRESENT) ||
+ !mfn_valid(mfn) )
 return;
 
 l2t = map_domain_page(mfn);
@@ -178,7 +179,8 @@ void show_page_walk(unsigned long addr)
 (l2e_get_flags(l2e) & _PAGE_PSE) ? "(PSE)" : "");
 unmap_domain_page(l2t);
 if ( !(l2e_get_flags(l2e) & _PAGE_PRESENT) ||
- (l2e_get_flags(l2e) & _PAGE_PSE) )
+ (l2e_get_flags(l2e) & _PAGE_PSE) ||
+ !mfn_valid(mfn) )
 return;
 
 l1t = map_domain_page(mfn);
--- 2009年07月10日.orig/xen/arch/x86/x86_64/mm.c 2009年07月10日 13:58:56.000000000 
+0200
+++ 2009年07月10日/xen/arch/x86/x86_64/mm.c 2009年07月17日 11:10:29.000000000 +0200
@@ -124,6 +124,7 @@ void *do_page_walk(struct vcpu *v, unsig
 l3e = l3t[l3_table_offset(addr)];
 mfn = l3e_get_pfn(l3e);
 if ( !(l3e_get_flags(l3e) & _PAGE_PRESENT) || !mfn_valid(mfn) )
+ return NULL;
 if ( (l3e_get_flags(l3e) & _PAGE_PSE) )
 return mfn_to_virt(mfn) + (addr & ((1UL << L3_PAGETABLE_SHIFT) - 1));
 
--- 2009年07月10日.orig/xen/arch/x86/x86_64/traps.c 2009年07月10日 13:58:56.000000000 
+0200
+++ 2009年07月10日/xen/arch/x86/x86_64/traps.c 2009年07月17日 11:11:59.000000000 
+0200
@@ -180,7 +180,8 @@ void show_page_walk(unsigned long addr)
 pfn = mfn_valid(mfn) ? get_gpfn_from_mfn(mfn) : INVALID_M2P_ENTRY;
 printk(" L4[0x%03lx] = %"PRIpte" %016lx\n",
 l4_table_offset(addr), l4e_get_intpte(l4e), pfn);
- if ( !(l4e_get_flags(l4e) & _PAGE_PRESENT) )
+ if ( !(l4e_get_flags(l4e) & _PAGE_PRESENT) ||
+ !mfn_valid(mfn) )
 return;
 
 l3t = mfn_to_virt(mfn);
@@ -192,7 +193,8 @@ void show_page_walk(unsigned long addr)
 l3_table_offset(addr), l3e_get_intpte(l3e), pfn,
 (l3e_get_flags(l3e) & _PAGE_PSE) ? " (PSE)" : "");
 if ( !(l3e_get_flags(l3e) & _PAGE_PRESENT) ||
- (l3e_get_flags(l3e) & _PAGE_PSE) )
+ (l3e_get_flags(l3e) & _PAGE_PSE) ||
+ !mfn_valid(mfn) )
 return;
 
 l2t = mfn_to_virt(mfn);
@@ -204,7 +206,8 @@ void show_page_walk(unsigned long addr)
 l2_table_offset(addr), l2e_get_intpte(l2e), pfn,
 (l2e_get_flags(l2e) & _PAGE_PSE) ? "(PSE)" : "");
 if ( !(l2e_get_flags(l2e) & _PAGE_PRESENT) ||
- (l2e_get_flags(l2e) & _PAGE_PSE) )
+ (l2e_get_flags(l2e) & _PAGE_PSE) ||
+ !mfn_valid(mfn) )
 return;
 
 l1t = mfn_to_virt(mfn);
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