KVM: MMU: only write protect mappings at pagetable level

If a pagetable contains a writeable large spte, all of its sptes will be
write protected, including non-leaf ones, leading to endless pagefaults.

Do not write protect pages above PT_PAGE_TABLE_LEVEL, as the spte fault
paths assume non-leaf sptes are writable.

Tested-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index b77a5ba398be..a2127f82e786 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3445,6 +3445,9 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot)
                 if (!test_bit(slot, sp->slot_bitmap))
                         continue;
 
+                if (sp->role.level != PT_PAGE_TABLE_LEVEL)
+                        continue;
+
                 pt = sp->spt;
                 for (i = 0; i < PT64_ENT_PER_PAGE; ++i)
                         /* avoid RMW */