KVM: x86/mmu: Move shadow-present check out of spte_has_volatile_bits()

Move the is_shadow_present_pte() check out of spte_has_volatile_bits()
and into its callers.  Well, caller, since only one of its two callers
doesn't already do the shadow-present check.

Opportunistically move the helper to spte.c/h so that it can be used by
the TDP MMU, which is also the primary motivation for the shadow-present
change.  Unlike the legacy MMU, the TDP MMU uses a single path for clear
leaf and non-leaf SPTEs, and to avoid unnecessary atomic updates, the TDP
MMU will need to check is_last_spte() prior to calling
spte_has_volatile_bits(), and calling is_last_spte() without first
calling is_shadow_present_spte() is at best odd, and at worst a violation
of KVM's loosely defines SPTE rules.

Note, mmu_spte_clear_track_bits() could likely skip the write entirely
for SPTEs that are not shadow-present.  Leave that cleanup for a future
patch to avoid introducing a functional change, and because the
shadow-present check can likely be moved further up the stack, e.g.
drop_large_spte() appears to be the only path that doesn't already
explicitly check for a shadow-present SPTE.

No functional change intended.

Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220423034752.1161007-3-seanjc@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 48dcb6a..311e4e1 100644 (file)
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -473,32 +473,6 @@ retry:
 }
 #endif
 
-static bool spte_has_volatile_bits(u64 spte)
-{
-       if (!is_shadow_present_pte(spte))
-               return false;
-
-       /*
-        * Always atomically update spte if it can be updated
-        * out of mmu-lock, it can ensure dirty bit is not lost,
-        * also, it can help us to get a stable is_writable_pte()
-        * to ensure tlb flush is not missed.
-        */
-       if (!is_writable_pte(spte) && is_mmu_writable_spte(spte))
-               return true;
-
-       if (is_access_track_spte(spte))
-               return true;
-
-       if (spte_ad_enabled(spte)) {
-               if (!(spte & shadow_accessed_mask) ||
-                   (is_writable_pte(spte) && !(spte & shadow_dirty_mask)))
-                       return true;
-       }
-
-       return false;
-}
-
 /* Rules for using mmu_spte_set:
  * Set the sptep from nonpresent to present.
  * Note: the sptep being assigned *must* be either not present
@@ -593,7 +567,8 @@ static int mmu_spte_clear_track_bits(struct kvm *kvm, u64 *sptep)
        u64 old_spte = *sptep;
        int level = sptep_to_sp(sptep)->role.level;
 
-       if (!spte_has_volatile_bits(old_spte))
+       if (!is_shadow_present_pte(old_spte) ||
+           !spte_has_volatile_bits(old_spte))
                __update_clear_spte_fast(sptep, 0ull);
        else
                old_spte = __update_clear_spte_slow(sptep, 0ull);

diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
index 4739b53..e5c0b6d 100644 (file)
--- a/arch/x86/kvm/mmu/spte.c
+++ b/arch/x86/kvm/mmu/spte.c
@@ -90,6 +90,34 @@ static bool kvm_is_mmio_pfn(kvm_pfn_t pfn)
                                     E820_TYPE_RAM);
 }
 
+/*
+ * Returns true if the SPTE has bits that may be set without holding mmu_lock.
+ * The caller is responsible for checking if the SPTE is shadow-present, and
+ * for determining whether or not the caller cares about non-leaf SPTEs.
+ */
+bool spte_has_volatile_bits(u64 spte)
+{
+       /*
+        * Always atomically update spte if it can be updated
+        * out of mmu-lock, it can ensure dirty bit is not lost,
+        * also, it can help us to get a stable is_writable_pte()
+        * to ensure tlb flush is not missed.
+        */
+       if (!is_writable_pte(spte) && is_mmu_writable_spte(spte))
+               return true;
+
+       if (is_access_track_spte(spte))
+               return true;
+
+       if (spte_ad_enabled(spte)) {
+               if (!(spte & shadow_accessed_mask) ||
+                   (is_writable_pte(spte) && !(spte & shadow_dirty_mask)))
+                       return true;
+       }
+
+       return false;
+}
+
 bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
               const struct kvm_memory_slot *slot,
               unsigned int pte_access, gfn_t gfn, kvm_pfn_t pfn,

diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
index c571784..80ab0f5 100644 (file)
--- a/arch/x86/kvm/mmu/spte.h
+++ b/arch/x86/kvm/mmu/spte.h
@@ -404,6 +404,8 @@ static inline u64 get_mmio_spte_generation(u64 spte)
        return gen;
 }
 
+bool spte_has_volatile_bits(u64 spte);
+
 bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
               const struct kvm_memory_slot *slot,
               unsigned int pte_access, gfn_t gfn, kvm_pfn_t pfn,