KVM: MMU: return page fault error code from permission_fault

This will help in the implementation of PKRU, where the PK bit of the page
fault error code cannot be computed in advance (unlike I/D, R/W and U/S).
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu.h

@@ -141,10 +141,14 @@ static inline bool is_write_protection(struct kvm_vcpu *vcpu)
 }
 
 /*
- * Will a fault with a given page-fault error code (pfec) cause a permission
- * fault with the given access (in ACC_* format)?
+ * 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
+ * access rights (in ACC_* format).
+ *
+ * Return zero if the access does not fault; return the page fault error code
+ * if the access faults.
  */
-static inline bool permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
+static inline u8 permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
 				  unsigned pte_access, unsigned pfec)
 {
 	int cpl = kvm_x86_ops->get_cpl(vcpu);
@@ -169,7 +173,8 @@ static inline bool permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
 
 	WARN_ON(pfec & PFERR_RSVD_MASK);
 
-	return (mmu->permissions[index] >> pte_access) & 1;
+	pfec |= PFERR_PRESENT_MASK;
+	return -((mmu->permissions[index] >> pte_access) & 1) & pfec;
 }
 
 void kvm_mmu_invalidate_zap_all_pages(struct kvm *kvm);

arch/x86/kvm/paging_tmpl.h

@@ -359,10 +359,9 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
 		walker->ptes[walker->level - 1] = pte;
 	} while (!is_last_gpte(mmu, walker->level, pte));
 
-	if (unlikely(permission_fault(vcpu, mmu, pte_access, access))) {
-		errcode |= PFERR_PRESENT_MASK;
+	errcode = permission_fault(vcpu, mmu, pte_access, access);
+	if (unlikely(errcode))
 		goto error;
-	}
 
 	gfn = gpte_to_gfn_lvl(pte, walker->level);
 	gfn += (addr & PT_LVL_OFFSET_MASK(walker->level)) >> PAGE_SHIFT;