[PATCH 2/4] x86: kvm: mmu: make spte mmio mask more explicit

[Peter Feiner <pfeiner@google.com>]

Specify both a mask (i.e., bits to consider) and a value (i.e.,
pattern of bits that indicates a special PTE) for mmio SPTEs. On
Intel, this lets us pack even more information into the
(SPTE_SPECIAL_MASK | EPT_VMX_RWX_MASK) mask we use for access
tracking liberating all (SPTE_SPECIAL_MASK | (non-misconfigured-RWX))
values.

Signed-off-by: Peter Feiner <pfeiner@google.com>
---
 arch/x86/kvm/mmu.c | 9 ++++++---
 arch/x86/kvm/mmu.h | 2 +-
 arch/x86/kvm/vmx.c | 3 ++-
 arch/x86/kvm/x86.c | 2 +-
 4 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index dfd4cd67e5a6..10b3cfc7b411 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -183,6 +183,7 @@ static u64 __read_mostly shadow_user_mask;
 static u64 __read_mostly shadow_accessed_mask;
 static u64 __read_mostly shadow_dirty_mask;
 static u64 __read_mostly shadow_mmio_mask;
+static u64 __read_mostly shadow_mmio_value;
 static u64 __read_mostly shadow_present_mask;
 
 /*
@@ -207,8 +208,10 @@ static const u64 shadow_acc_track_saved_bits_shift = PT64_SECOND_AVAIL_BITS_SHIF
 static void mmu_spte_set(u64 *sptep, u64 spte);
 static void mmu_free_roots(struct kvm_vcpu *vcpu);
 
-void kvm_mmu_set_mmio_spte_mask(u64 mmio_mask)
+void kvm_mmu_set_mmio_spte_mask(u64 mmio_mask, u64 mmio_value)
 {
+	BUG_ON((mmio_mask & mmio_value) != mmio_value);
+	shadow_mmio_value = mmio_value | SPTE_SPECIAL_MASK;
 	shadow_mmio_mask = mmio_mask | SPTE_SPECIAL_MASK;
 }
 EXPORT_SYMBOL_GPL(kvm_mmu_set_mmio_spte_mask);
@@ -270,7 +273,7 @@ static void mark_mmio_spte(struct kvm_vcpu *vcpu, u64 *sptep, u64 gfn,
 	u64 mask = generation_mmio_spte_mask(gen);
 
 	access &= ACC_WRITE_MASK | ACC_USER_MASK;
-	mask |= shadow_mmio_mask | access | gfn << PAGE_SHIFT;
+	mask |= shadow_mmio_value | access | gfn << PAGE_SHIFT;
 
 	trace_mark_mmio_spte(sptep, gfn, access, gen);
 	mmu_spte_set(sptep, mask);
@@ -278,7 +281,7 @@ static void mark_mmio_spte(struct kvm_vcpu *vcpu, u64 *sptep, u64 gfn,
 
 static bool is_mmio_spte(u64 spte)
 {
-	return (spte & shadow_mmio_mask) == shadow_mmio_mask;
+	return (spte & shadow_mmio_mask) == shadow_mmio_value;
 }
 
 static gfn_t get_mmio_spte_gfn(u64 spte)
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 27975807cc64..41d362e95681 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -51,7 +51,7 @@ static inline u64 rsvd_bits(int s, int e)
 	return ((1ULL << (e - s + 1)) - 1) << s;
 }
 
-void kvm_mmu_set_mmio_spte_mask(u64 mmio_mask);
+void kvm_mmu_set_mmio_spte_mask(u64 mmio_mask, u64 mmio_value);
 
 void
 reset_shadow_zero_bits_mask(struct kvm_vcpu *vcpu, struct kvm_mmu *context);
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index c6dec552b28f..e59b01a1d431 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -5163,7 +5163,8 @@ static void ept_set_mmio_spte_mask(void)
 	 * EPT Misconfigurations can be generated if the value of bits 2:0
 	 * of an EPT paging-structure entry is 110b (write/execute).
 	 */
-	kvm_mmu_set_mmio_spte_mask(VMX_EPT_MISCONFIG_WX_VALUE);
+	kvm_mmu_set_mmio_spte_mask(VMX_EPT_RWX_MASK,
+				   VMX_EPT_MISCONFIG_WX_VALUE);
 }
 
 #define VMX_XSS_EXIT_BITMAP 0
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a2cd0997343c..ac6eb99b99b5 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6009,7 +6009,7 @@ static void kvm_set_mmio_spte_mask(void)
 		mask &= ~1ull;
 #endif
 
-	kvm_mmu_set_mmio_spte_mask(mask);
+	kvm_mmu_set_mmio_spte_mask(mask, mask);
 }
 
 #ifdef CONFIG_X86_64
-- 
2.13.2.725.g09c95d1e9-goog