summaryrefslogtreecommitdiff
path: root/arch/x86/kvm/mmu/spte.h
diff options
context:
space:
mode:
Diffstat (limited to 'arch/x86/kvm/mmu/spte.h')
-rw-r--r--arch/x86/kvm/mmu/spte.h42
1 files changed, 36 insertions, 6 deletions
diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
index a4af2a42695c..be6a007a4af3 100644
--- a/arch/x86/kvm/mmu/spte.h
+++ b/arch/x86/kvm/mmu/spte.h
@@ -60,10 +60,6 @@ static_assert(SPTE_TDP_AD_ENABLED_MASK == 0);
(((address) >> PT64_LEVEL_SHIFT(level)) & ((1 << PT64_LEVEL_BITS) - 1))
#define SHADOW_PT_INDEX(addr, level) PT64_INDEX(addr, level)
-/* Bits 9 and 10 are ignored by all non-EPT PTEs. */
-#define DEFAULT_SPTE_HOST_WRITEABLE BIT_ULL(9)
-#define DEFAULT_SPTE_MMU_WRITEABLE BIT_ULL(10)
-
/*
* The mask/shift to use for saving the original R/X bits when marking the PTE
* as not-present for access tracking purposes. We do not save the W bit as the
@@ -79,6 +75,35 @@ static_assert(SPTE_TDP_AD_ENABLED_MASK == 0);
static_assert(!(SPTE_TDP_AD_MASK & SHADOW_ACC_TRACK_SAVED_MASK));
/*
+ * *_SPTE_HOST_WRITEABLE (aka Host-writable) indicates whether the host permits
+ * writes to the guest page mapped by the SPTE. This bit is cleared on SPTEs
+ * that map guest pages in read-only memslots and read-only VMAs.
+ *
+ * Invariants:
+ * - If Host-writable is clear, PT_WRITABLE_MASK must be clear.
+ *
+ *
+ * *_SPTE_MMU_WRITEABLE (aka MMU-writable) indicates whether the shadow MMU
+ * allows writes to the guest page mapped by the SPTE. This bit is cleared when
+ * the guest page mapped by the SPTE contains a page table that is being
+ * monitored for shadow paging. In this case the SPTE can only be made writable
+ * by unsyncing the shadow page under the mmu_lock.
+ *
+ * Invariants:
+ * - If MMU-writable is clear, PT_WRITABLE_MASK must be clear.
+ * - If MMU-writable is set, Host-writable must be set.
+ *
+ * If MMU-writable is set, PT_WRITABLE_MASK is normally set but can be cleared
+ * to track writes for dirty logging. For such SPTEs, KVM will locklessly set
+ * PT_WRITABLE_MASK upon the next write from the guest and record the write in
+ * the dirty log (see fast_page_fault()).
+ */
+
+/* Bits 9 and 10 are ignored by all non-EPT PTEs. */
+#define DEFAULT_SPTE_HOST_WRITEABLE BIT_ULL(9)
+#define DEFAULT_SPTE_MMU_WRITEABLE BIT_ULL(10)
+
+/*
* Low ignored bits are at a premium for EPT, use high ignored bits, taking care
* to not overlap the A/D type mask or the saved access bits of access-tracked
* SPTEs when A/D bits are disabled.
@@ -316,8 +341,13 @@ static __always_inline bool is_rsvd_spte(struct rsvd_bits_validate *rsvd_check,
static inline bool spte_can_locklessly_be_made_writable(u64 spte)
{
- return (spte & shadow_host_writable_mask) &&
- (spte & shadow_mmu_writable_mask);
+ if (spte & shadow_mmu_writable_mask) {
+ WARN_ON_ONCE(!(spte & shadow_host_writable_mask));
+ return true;
+ }
+
+ WARN_ON_ONCE(spte & PT_WRITABLE_MASK);
+ return false;
}
static inline u64 get_mmio_spte_generation(u64 spte)