[PATCH v5 06/14] nEPT: Support shadow paging for guest paging without A/D bits

Gleb Natapov
2013-07-31T14:49:09Z

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.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
---
arch/x86/kvm/paging_tmpl.h | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 7581395..2c2f635 100644
--- 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);
--
1.7.10.4