KVM: x86/mmu: Add helper to convert SPTE value to its shadow page

Add a helper to convert a SPTE to its shadow page to deduplicate a
variety of flows and hopefully avoid future bugs, e.g. if KVM attempts to
get the shadow page for a SPTE without dropping high bits.

Opportunistically add a comment in mmu_free_root_page() documenting why
it treats the root HPA as a SPTE.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221019165618.927057-7-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 e384b78..5f9b57c 100644 (file)
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1819,7 +1819,7 @@ static int __mmu_unsync_walk(struct kvm_mmu_page *sp,
                        continue;
                }
 
-               child = to_shadow_page(ent & SPTE_BASE_ADDR_MASK);
+               child = spte_to_child_sp(ent);
 
                if (child->unsync_children) {
                        if (mmu_pages_add(pvec, child, i))
@@ -2378,7 +2378,7 @@ static void validate_direct_spte(struct kvm_vcpu *vcpu, u64 *sptep,
                 * so we should update the spte at this point to get
                 * a new sp with the correct access.
                 */
-               child = to_shadow_page(*sptep & SPTE_BASE_ADDR_MASK);
+               child = spte_to_child_sp(*sptep);
                if (child->role.access == direct_access)
                        return;
 
@@ -2399,7 +2399,7 @@ static int mmu_page_zap_pte(struct kvm *kvm, struct kvm_mmu_page *sp,
                if (is_last_spte(pte, sp->role.level)) {
                        drop_spte(kvm, spte);
                } else {
-                       child = to_shadow_page(pte & SPTE_BASE_ADDR_MASK);
+                       child = spte_to_child_sp(pte);
                        drop_parent_pte(child, spte);
 
                        /*
@@ -2838,7 +2838,7 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, struct kvm_memory_slot *slot,
                        struct kvm_mmu_page *child;
                        u64 pte = *sptep;
 
-                       child = to_shadow_page(pte & SPTE_BASE_ADDR_MASK);
+                       child = spte_to_child_sp(pte);
                        drop_parent_pte(child, sptep);
                        flush = true;
                } else if (pfn != spte_to_pfn(*sptep)) {
@@ -3455,7 +3455,11 @@ static void mmu_free_root_page(struct kvm *kvm, hpa_t *root_hpa,
        if (!VALID_PAGE(*root_hpa))
                return;
 
-       sp = to_shadow_page(*root_hpa & SPTE_BASE_ADDR_MASK);
+       /*
+        * The "root" may be a special root, e.g. a PAE entry, treat it as a
+        * SPTE to ensure any non-PA bits are dropped.
+        */
+       sp = spte_to_child_sp(*root_hpa);
        if (WARN_ON(!sp))
                return;
 
@@ -3940,8 +3944,7 @@ void kvm_mmu_sync_roots(struct kvm_vcpu *vcpu)
                hpa_t root = vcpu->arch.mmu->pae_root[i];
 
                if (IS_VALID_PAE_ROOT(root)) {
-                       root &= SPTE_BASE_ADDR_MASK;
-                       sp = to_shadow_page(root);
+                       sp = spte_to_child_sp(root);
                        mmu_sync_children(vcpu, sp, true);
                }
        }

diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index 2215224..dbaf675 100644 (file)
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -133,18 +133,6 @@ struct kvm_mmu_page {
 
 extern struct kmem_cache *mmu_page_header_cache;
 
-static inline struct kvm_mmu_page *to_shadow_page(hpa_t shadow_page)
-{
-       struct page *page = pfn_to_page(shadow_page >> PAGE_SHIFT);
-
-       return (struct kvm_mmu_page *)page_private(page);
-}
-
-static inline struct kvm_mmu_page *sptep_to_sp(u64 *sptep)
-{
-       return to_shadow_page(__pa(sptep));
-}
-
 static inline int kvm_mmu_role_as_id(union kvm_mmu_page_role role)
 {
        return role.smm ? 1 : 0;

diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
index 79560d7..1f03701 100644 (file)
--- a/arch/x86/kvm/mmu/spte.h
+++ b/arch/x86/kvm/mmu/spte.h
@@ -219,6 +219,23 @@ static inline int spte_index(u64 *sptep)
  */
 extern u64 __read_mostly shadow_nonpresent_or_rsvd_lower_gfn_mask;
 
+static inline struct kvm_mmu_page *to_shadow_page(hpa_t shadow_page)
+{
+       struct page *page = pfn_to_page((shadow_page) >> PAGE_SHIFT);
+
+       return (struct kvm_mmu_page *)page_private(page);
+}
+
+static inline struct kvm_mmu_page *spte_to_child_sp(u64 spte)
+{
+       return to_shadow_page(spte & SPTE_BASE_ADDR_MASK);
+}
+
+static inline struct kvm_mmu_page *sptep_to_sp(u64 *sptep)
+{
+       return to_shadow_page(__pa(sptep));
+}
+
 static inline bool is_mmio_spte(u64 spte)
 {
        return (spte & shadow_mmio_mask) == shadow_mmio_value &&

diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
index c163f7c..d371420 100644 (file)
--- a/arch/x86/kvm/mmu/tdp_mmu.h
+++ b/arch/x86/kvm/mmu/tdp_mmu.h
@@ -5,6 +5,8 @@
 
 #include <linux/kvm_host.h>
 
+#include "spte.h"
+
 hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu);
 
 __must_check static inline bool kvm_tdp_mmu_get_root(struct kvm_mmu_page *root)