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, 0 deletions

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 9f1b4711d5ea..0f9e0e95f365 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -529,6 +529,7 @@ static u64 mmu_spte_update_no_track(u64 *sptep, u64 new_spte)
 	u64 old_spte = *sptep;
 
 	WARN_ON(!is_shadow_present_pte(new_spte));
+	check_spte_writable_invariants(new_spte);
 
 	if (!is_shadow_present_pte(old_spte)) {
 		mmu_spte_set(sptep, new_spte);