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>

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 9f1b471..0f9e0e9 100644 (file)
--- 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);

diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
index 73cfe62..788d9d2 100644 (file)
--- a/arch/x86/kvm/mmu/spte.c
+++ b/arch/x86/kvm/mmu/spte.c
@@ -250,14 +250,7 @@ u64 mark_spte_for_access_track(u64 spte)
        if (is_access_track_spte(spte))
                return spte;
 
-       /*
-        * Making an Access Tracking PTE will result in removal of write access
-        * from the PTE. So, verify that we will be able to restore the write
-        * access in the fast page fault path later on.
-        */
-       WARN_ONCE((spte & PT_WRITABLE_MASK) &&
-                 !spte_can_locklessly_be_made_writable(spte),
-                 "kvm: Writable SPTE is not locklessly dirty-trackable\n");
+       check_spte_writable_invariants(spte);
 
        WARN_ONCE(spte & (SHADOW_ACC_TRACK_SAVED_BITS_MASK <<
                          SHADOW_ACC_TRACK_SAVED_BITS_SHIFT),

diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
index 912e668..b8fd055 100644 (file)
--- 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;
 }
 

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index be80833..8ad5b37 100644 (file)
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -452,6 +452,9 @@ static void __handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
 
        trace_kvm_tdp_mmu_spte_changed(as_id, gfn, level, old_spte, new_spte);
 
+       if (is_leaf)
+               check_spte_writable_invariants(new_spte);
+
        /*
         * The only times a SPTE should be changed from a non-present to
         * non-present state is when an MMIO entry is installed/modified/