KVM: x86/mmu: Move is_writable_pte() to spte.h

Move is_writable_pte() close to the other functions that check
writability information about SPTEs. While here opportunistically
replace the open-coded bit arithmetic in
check_spte_writable_invariants() with a call to is_writable_pte().

No functional change intended.
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20220125230518.1697048-4-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu.h

@@ -202,44 +202,6 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 	return vcpu->arch.mmu->page_fault(vcpu, &fault);
 }
 
-/*
- * Currently, we have two sorts of write-protection, a) the first one
- * write-protects guest page to sync the guest modification, b) another one is
- * used to sync dirty bitmap when we do KVM_GET_DIRTY_LOG. The differences
- * between these two sorts are:
- * 1) the first case clears MMU-writable bit.
- * 2) the first case requires flushing tlb immediately avoiding corrupting
- *    shadow page table between all vcpus so it should be in the protection of
- *    mmu-lock. And the another case does not need to flush tlb until returning
- *    the dirty bitmap to userspace since it only write-protects the page
- *    logged in the bitmap, that means the page in the dirty bitmap is not
- *    missed, so it can flush tlb out of mmu-lock.
- *
- * So, there is the problem: the first case can meet the corrupted tlb caused
- * by another case which write-protects pages but without flush tlb
- * immediately. In order to making the first case be aware this problem we let
- * it flush tlb if we try to write-protect a spte whose MMU-writable bit
- * is set, it works since another case never touches MMU-writable bit.
- *
- * Anyway, whenever a spte is updated (only permission and status bits are
- * changed) we need to check whether the spte with MMU-writable becomes
- * readonly, if that happens, we need to flush tlb. Fortunately,
- * mmu_spte_update() has already handled it perfectly.
- *
- * The rules to use MMU-writable and PT_WRITABLE_MASK:
- * - if we want to see if it has writable tlb entry or if the spte can be
- *   writable on the mmu mapping, check MMU-writable, this is the most
- *   case, otherwise
- * - if we fix page fault on the spte or do write-protection by dirty logging,
- *   check PT_WRITABLE_MASK.
- *
- * TODO: introduce APIs to split these two cases.
- */
-static inline bool is_writable_pte(unsigned long pte)
-{
-	return pte & PT_WRITABLE_MASK;
-}
-
 /*
  * Check if a given access (described through the I/D, W/R and U/S bits of a
  * page fault error code pfec) causes a permission fault with the given PTE

arch/x86/kvm/mmu/spte.h

@@ -339,6 +339,44 @@ static __always_inline bool is_rsvd_spte(struct rsvd_bits_validate *rsvd_check,
 	       __is_rsvd_bits_set(rsvd_check, spte, level);
 }
 
+/*
+ * Currently, we have two sorts of write-protection, a) the first one
+ * write-protects guest page to sync the guest modification, b) another one is
+ * used to sync dirty bitmap when we do KVM_GET_DIRTY_LOG. The differences
+ * between these two sorts are:
+ * 1) the first case clears MMU-writable bit.
+ * 2) the first case requires flushing tlb immediately avoiding corrupting
+ *    shadow page table between all vcpus so it should be in the protection of
+ *    mmu-lock. And the another case does not need to flush tlb until returning
+ *    the dirty bitmap to userspace since it only write-protects the page
+ *    logged in the bitmap, that means the page in the dirty bitmap is not
+ *    missed, so it can flush tlb out of mmu-lock.
+ *
+ * So, there is the problem: the first case can meet the corrupted tlb caused
+ * by another case which write-protects pages but without flush tlb
+ * immediately. In order to making the first case be aware this problem we let
+ * it flush tlb if we try to write-protect a spte whose MMU-writable bit
+ * is set, it works since another case never touches MMU-writable bit.
+ *
+ * Anyway, whenever a spte is updated (only permission and status bits are
+ * changed) we need to check whether the spte with MMU-writable becomes
+ * readonly, if that happens, we need to flush tlb. Fortunately,
+ * mmu_spte_update() has already handled it perfectly.
+ *
+ * The rules to use MMU-writable and PT_WRITABLE_MASK:
+ * - if we want to see if it has writable tlb entry or if the spte can be
+ *   writable on the mmu mapping, check MMU-writable, this is the most
+ *   case, otherwise
+ * - if we fix page fault on the spte or do write-protection by dirty logging,
+ *   check PT_WRITABLE_MASK.
+ *
+ * TODO: introduce APIs to split these two cases.
+ */
+static inline bool is_writable_pte(unsigned long pte)
+{
+	return pte & PT_WRITABLE_MASK;
+}
+
 /* Note: spte must be a shadow-present leaf SPTE. */
 static inline void check_spte_writable_invariants(u64 spte)
 {
@@ -347,7 +385,7 @@ static inline void check_spte_writable_invariants(u64 spte)
 			  "kvm: MMU-writable SPTE is not Host-writable: %llx",
 			  spte);
 	else
-		WARN_ONCE(spte & PT_WRITABLE_MASK,
+		WARN_ONCE(is_writable_pte(spte),
 			  "kvm: Writable SPTE is not MMU-writable: %llx", spte);
 }