diff mbox series

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

Message ID 20220723012325.1715714-6-seanjc@google.com (mailing list archive)
State New, archived
Headers show
Series KVM: x86: Apply NX mitigation more precisely | expand

Commit Message

Sean Christopherson July 23, 2022, 1:23 a.m. UTC 
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(-)

Comments

David Matlack July 25, 2022, 11:23 p.m. UTC | #1 
On Sat, Jul 23, 2022 at 01:23:24AM +0000, Sean Christopherson wrote:
> 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>
> ---
[...]
> --- 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);
> +}

spte_to_sp() and sptep_to_sp() are a bit hard to differentiate visually.

Maybe spte_to_child_sp() or to_child_sp()?

> +
> +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
>
Sean Christopherson July 25, 2022, 11:33 p.m. UTC | #2 
On Mon, Jul 25, 2022, David Matlack wrote:
> On Sat, Jul 23, 2022 at 01:23:24AM +0000, Sean Christopherson wrote:
> > 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>
> > ---
> [...]
> > --- 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);
> > +}
> 
> spte_to_sp() and sptep_to_sp() are a bit hard to differentiate visually.

Yeah, I balked a bit when making the change, but couldn't come up with a better
alternative.

> Maybe spte_to_child_sp() or to_child_sp()?

I like to_child_sp().  Apparently I have a mental block when it comes to parent
vs. child pages and never realized that sptep_to_sp() gets the "parent" but
spte_to_sp() gets the "child".  That indeed makes spte_to_sp() a bad name.
diff mbox series

Patch

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)