KVM: MMU: fix infinite fault access retry
We have two issues in current code:
- if target gfn is used as its page table, guest will refault then kvm will use
small page size to map it. We need two #PF to fix its shadow page table
- sometimes, say a exception is triggered during vm-exit caused by #PF
(see handle_exception() in vmx.c), we remove all the shadow pages shadowed
by the target gfn before go into page fault path, it will cause infinite
loop:
delete shadow pages shadowed by the gfn -> try to use large page size to map
the gfn -> retry the access ->...
To fix these, we can adjust page size early if the target gfn is used as page
table
Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 2a3c890..54fc61e 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2380,15 +2380,10 @@
if (pte_access & ACC_WRITE_MASK) {
/*
- * There are two cases:
- * - the one is other vcpu creates new sp in the window
- * between mapping_level() and acquiring mmu-lock.
- * - the another case is the new sp is created by itself
- * (page-fault path) when guest uses the target gfn as
- * its page table.
- * Both of these cases can be fixed by allowing guest to
- * retry the access, it will refault, then we can establish
- * the mapping by using small page.
+ * Other vcpu creates new sp in the window between
+ * mapping_level() and acquiring mmu-lock. We can
+ * allow guest to retry the access, the mapping can
+ * be fixed if guest refault.
*/
if (level > PT_PAGE_TABLE_LEVEL &&
has_wrprotected_page(vcpu->kvm, gfn, level))