Check only the terminal leaf for a "!PRESENT || MMIO" SPTE when looking
for reserved bits on valid, non-MMIO SPTEs. The get_walk() helpers
terminate their walks if a not-present or MMIO SPTE is encountered, i.e.
the non-terminal SPTEs have already been verified to be regular SPTEs.
This eliminates an extra check-and-branch in a relatively hot loop.
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/mmu/mmu.c | 20 +++++++++++++-------
1 file changed, 13 insertions(+), 7 deletions(-)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 4798a4472066..769855f5f0a1 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3511,7 +3511,7 @@ static int get_walk(struct kvm_vcpu *vcpu, u64 addr, u64 *sptes, int *root_level
return leaf;
}
-/* return true if reserved bit is detected on spte. */
+/* return true if reserved bit(s) are detected on a valid, non-MMIO SPTE. */
static bool get_mmio_spte(struct kvm_vcpu *vcpu, u64 addr, u64 *sptep)
{
u64 sptes[PT64_ROOT_MAX_LEVEL + 1];
@@ -3534,11 +3534,20 @@ static bool get_mmio_spte(struct kvm_vcpu *vcpu, u64 addr, u64 *sptep)
return reserved;
}
+ *sptep = sptes[leaf];
+
+ /*
+ * Skip reserved bits checks on the terminal leaf if it's not a valid
+ * SPTE. Note, this also (intentionally) skips MMIO SPTEs, which, by
+ * design, always have reserved bits set. The purpose of the checks is
+ * to detect reserved bits on non-MMIO SPTEs. i.e. buggy SPTEs.
+ */
+ if (!is_shadow_present_pte(sptes[leaf]))
+ leaf++;
+
rsvd_check = &vcpu->arch.mmu->shadow_zero_check;
- for (level = root; level >= leaf; level--) {
- if (!is_shadow_present_pte(sptes[level]))
- break;
+ for (level = root; level >= leaf; level--)
/*
* Use a bitwise-OR instead of a logical-OR to aggregate the
* reserved bit and EPT's invalid memtype/XWR checks to avoid
@@ -3546,7 +3555,6 @@ static bool get_mmio_spte(struct kvm_vcpu *vcpu, u64 addr, u64 *sptep)
*/
reserved |= __is_bad_mt_xwr(rsvd_check, sptes[level]) |
__is_rsvd_bits_set(rsvd_check, sptes[level], level);
- }
if (reserved) {
pr_err("%s: detect reserved bits on spte, addr 0x%llx, dump hierarchy:\n",
@@ -3556,8 +3564,6 @@ static bool get_mmio_spte(struct kvm_vcpu *vcpu, u64 addr, u64 *sptep)
sptes[level], level);
}
- *sptep = sptes[leaf];
-
return reserved;
}
--
2.29.2.684.gfbc64c5ab5-goog
