KVM: x86/mmu: Check SPTE writable invariants when setting leaf SPTEs

Check SPTE writable invariants when setting SPTEs rather than in
spte_can_locklessly_be_made_writable(). By the time KVM checks
spte_can_locklessly_be_made_writable(), the SPTE has long been since
corrupted.

Note that these invariants only apply to shadow-present leaf SPTEs (i.e.
not to MMIO SPTEs, non-leaf SPTEs, etc.). Add a comment explaining the
restriction and only instrument the code paths that set shadow-present
leaf SPTEs.

To account for access tracking, also check the SPTE writable invariants
when marking an SPTE as an access track SPTE. This also lets us remove
a redundant WARN from mark_spte_for_access_track().

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20220125230518.1697048-3-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
index 912e66859ea0..b8fd055acdbd 100644
--- a/arch/x86/kvm/mmu/spte.h
+++ b/arch/x86/kvm/mmu/spte.h
@@ -339,6 +339,7 @@ static __always_inline bool is_rsvd_spte(struct rsvd_bits_validate *rsvd_check,
 	       __is_rsvd_bits_set(rsvd_check, spte, level);
 }
 
+/* Note: spte must be a shadow-present leaf SPTE. */
 static inline void check_spte_writable_invariants(u64 spte)
 {
 	if (spte & shadow_mmu_writable_mask)
@@ -352,7 +353,6 @@ static inline void check_spte_writable_invariants(u64 spte)
 
 static inline bool spte_can_locklessly_be_made_writable(u64 spte)
 {
-	check_spte_writable_invariants(spte);
 	return spte & shadow_mmu_writable_mask;
 }