[PATCH v2 5/6] KVM: x86/mmu: Add helper to convert SPTE value to its shadow page

Sean Christopherson
2022-07-23T01:23:59Z

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>
---
arch/x86/kvm/mmu/mmu.c | 17 ++++++++++-------
arch/x86/kvm/mmu/mmu_internal.h | 12 ------------
arch/x86/kvm/mmu/spte.h | 17 +++++++++++++++++
arch/x86/kvm/mmu/tdp_mmu.h | 2 ++
4 files changed, 29 insertions(+), 19 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index e9252e7cd5a2..ed3cfb31853b 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1798,7 +1798,7 @@ static int __mmu_unsync_walk(struct kvm_mmu_page *sp,
continue;
}

- child = to_shadow_page(ent & SPTE_BASE_ADDR_MASK);
+ child = spte_to_sp(ent);

if (child->unsync_children) {
if (mmu_pages_add(pvec, child, i))
@@ -2357,7 +2357,7 @@ 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_sp(*sptep);
if (child->role.access == direct_access)
return;

@@ -2378,7 +2378,7 @@ 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_sp(pte);
drop_parent_pte(child, spte);

/*
@@ -2817,7 +2817,7 @@ 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_sp(pte);
drop_parent_pte(child, sptep);
flush = true;
} else if (pfn != spte_to_pfn(*sptep)) {
@@ -3429,7 +3429,11 @@ 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_sp(*root_hpa);
if (WARN_ON(!sp))
return;

@@ -3914,8 +3918,7 @@ 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_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 2a887d08b722..04457b5ec968 100644
--- 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 cabe3fbb4f39..a240b7eca54f 100644
--- a/arch/x86/kvm/mmu/spte.h
+++ b/arch/x86/kvm/mmu/spte.h
@@ -207,6 +207,23 @@ 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_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 c163f7cc23ca..d3714200b932 100644
--- 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)
--
2.37.1.359.gd136c6c3e2-goog