KVM: MMU: Add validate_direct_spte() helper

Add a helper to verify that a direct shadow page is valid wrt the required
access permissions; drop the page if it is not valid.

Reviewed-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

2 files changed, 29 insertions, 21 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index b75d6cb44ab6..36c62f33513f 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1500,6 +1500,29 @@ static void drop_large_spte(struct kvm_vcpu *vcpu, u64 *sptep)
         }
 }
 
+static void validate_direct_spte(struct kvm_vcpu *vcpu, u64 *sptep,
+                                   unsigned direct_access)
+{
+        if (is_shadow_present_pte(*sptep) && !is_large_pte(*sptep)) {
+                struct kvm_mmu_page *child;
+
+                /*
+                 * For the direct sp, if the guest pte's dirty bit
+                 * changed form clean to dirty, it will corrupt the
+                 * sp's access: allow writable in the read-only sp,
+                 * so we should update the spte at this point to get
+                 * a new sp with the correct access.
+                 */
+                child = page_header(*sptep & PT64_BASE_ADDR_MASK);
+                if (child->role.access == direct_access)
+                        return;
+
+                mmu_page_remove_parent_pte(child, sptep);
+                __set_spte(sptep, shadow_trap_nonpresent_pte);
+                kvm_flush_remote_tlbs(vcpu->kvm);
+        }
+}
+
 static void kvm_mmu_page_unlink_children(struct kvm *kvm,
                                          struct kvm_mmu_page *sp)
 {
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 0fb7068d64c7..0c7461d3a5be 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -338,30 +338,15 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
                         break;
                 }
 
-                if (is_shadow_present_pte(*sptep) && !is_large_pte(*sptep)) {
-                        struct kvm_mmu_page *child;
-
-                        if (level != gw->level)
-                                continue;
-
-                        /*
-                         * For the direct sp, if the guest pte's dirty bit
-                         * changed form clean to dirty, it will corrupt the
-                         * sp's access: allow writable in the read-only sp,
-                         * so we should update the spte at this point to get
-                         * a new sp with the correct access.
-                         */
-                        child = page_header(*sptep & PT64_BASE_ADDR_MASK);
-                        if (child->role.access == direct_access)
-                                continue;
-
-                        mmu_page_remove_parent_pte(child, sptep);
-                        __set_spte(sptep, shadow_trap_nonpresent_pte);
-                        kvm_flush_remote_tlbs(vcpu->kvm);
-                }
+                if (is_shadow_present_pte(*sptep) && !is_large_pte(*sptep)
+                    && level == gw->level)
+                        validate_direct_spte(vcpu, sptep, direct_access);
 
                 drop_large_spte(vcpu, sptep);
 
+                if (is_shadow_present_pte(*sptep))
+                        continue;
+
                 if (level <= gw->level) {
                         direct = 1;
                         access = direct_access;