nEPT: Support shadow paging for guest paging without A/D bits

Some guest paging modes do not support A/D bits. Add support for such
modes in shadow page code. For such modes PT_GUEST_DIRTY_MASK,
PT_GUEST_ACCESSED_MASK, PT_GUEST_DIRTY_SHIFT and PT_GUEST_ACCESSED_SHIFT
should be set to zero.

Reviewed-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 83702a68e98723f1097d6a276fc052f966f7787b..656f7fae312a8b887dc7c2eabf8fef0771fb5a85 100644 (file)
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -92,6 +92,10 @@ static inline void FNAME(protect_clean_gpte)(unsigned *access, unsigned gpte)
 {
        unsigned mask;
 
+       /* dirty bit is not supported, so no need to track it */
+       if (!PT_GUEST_DIRTY_MASK)
+               return;
+
        BUILD_BUG_ON(PT_WRITABLE_MASK != ACC_WRITE_MASK);
 
        mask = (unsigned)~ACC_WRITE_MASK;
@@ -147,7 +151,8 @@ static bool FNAME(prefetch_invalid_gpte)(struct kvm_vcpu *vcpu,
        if (!FNAME(is_present_gpte)(gpte))
                goto no_present;
 
-       if (!(gpte & PT_GUEST_ACCESSED_MASK))
+       /* if accessed bit is not supported prefetch non accessed gpte */
+       if (PT_GUEST_ACCESSED_MASK && !(gpte & PT_GUEST_ACCESSED_MASK))
                goto no_present;
 
        return false;
@@ -178,6 +183,10 @@ static int FNAME(update_accessed_dirty_bits)(struct kvm_vcpu *vcpu,
        gfn_t table_gfn;
        int ret;
 
+       /* dirty/accessed bits are not supported, so no need to update them */
+       if (!PT_GUEST_DIRTY_MASK)
+               return 0;
+
        for (level = walker->max_level; level >= walker->level; --level) {
                pte = orig_pte = walker->ptes[level - 1];
                table_gfn = walker->table_gfn[level - 1];
@@ -316,8 +325,9 @@ retry_walk:
                FNAME(protect_clean_gpte)(&pte_access, pte);
        else
                /*
-                * On a write fault, fold the dirty bit into accessed_dirty by
-                * shifting it one place right.
+                * On a write fault, fold the dirty bit into accessed_dirty.
+                * For modes without A/D bits support accessed_dirty will be
+                * always clear.
                 */
                accessed_dirty &= pte >>
                        (PT_GUEST_DIRTY_SHIFT - PT_GUEST_ACCESSED_SHIFT);