[RFC PATCH v3 34/59] KVM: x86/mmu: Allow non-zero init value for shadow PTE

[isaku . yamahata]

From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>

TDX will run with EPT violation #VEs enabled, which means KVM needs to
set the "suppress #VE" bit in unused PTEs to avoid unintentionally
reflecting not-present EPT violations into the guest.

Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
---
 arch/x86/kvm/mmu.h      |  1 +
 arch/x86/kvm/mmu/mmu.c  | 50 +++++++++++++++++++++++++++++++++++------
 arch/x86/kvm/mmu/spte.c | 10 +++++++++
 arch/x86/kvm/mmu/spte.h |  2 ++
 4 files changed, 56 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 583483bb6f71..79ccee8bbc38 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -66,6 +66,7 @@ static __always_inline u64 rsvd_bits(int s, int e)
 
 void kvm_mmu_set_mmio_spte_mask(u64 mmio_value, u64 mmio_mask, u64 access_mask);
 void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only);
+void kvm_mmu_set_spte_init_value(u64 init_value);
 
 void kvm_init_mmu(struct kvm_vcpu *vcpu);
 void kvm_init_shadow_npt_mmu(struct kvm_vcpu *vcpu, unsigned long cr0,
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 01569913f1f0..510991c2e94e 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -623,9 +623,9 @@ static int mmu_spte_clear_track_bits(struct kvm *kvm, u64 *sptep)
 	int level = sptep_to_sp(sptep)->role.level;
 
 	if (!spte_has_volatile_bits(old_spte))
-		__update_clear_spte_fast(sptep, 0ull);
+		__update_clear_spte_fast(sptep, shadow_init_value);
 	else
-		old_spte = __update_clear_spte_slow(sptep, 0ull);
+		old_spte = __update_clear_spte_slow(sptep, shadow_init_value);
 
 	if (!is_shadow_present_pte(old_spte))
 		return old_spte;
@@ -657,7 +657,7 @@ static int mmu_spte_clear_track_bits(struct kvm *kvm, u64 *sptep)
  */
 static void mmu_spte_clear_no_track(u64 *sptep)
 {
-	__update_clear_spte_fast(sptep, 0ull);
+	__update_clear_spte_fast(sptep, shadow_init_value);
 }
 
 static u64 mmu_spte_get_lockless(u64 *sptep)
@@ -743,6 +743,42 @@ static void walk_shadow_page_lockless_end(struct kvm_vcpu *vcpu)
 	}
 }
 
+static inline void kvm_init_shadow_page(void *page)
+{
+#ifdef CONFIG_X86_64
+	int ign;
+
+	asm volatile (
+		"rep stosq\n\t"
+		: "=c"(ign), "=D"(page)
+		: "a"(shadow_init_value), "c"(4096/8), "D"(page)
+		: "memory"
+	);
+#else
+	BUG();
+#endif
+}
+
+static int mmu_topup_shadow_page_cache(struct kvm_vcpu *vcpu)
+{
+	struct kvm_mmu_memory_cache *mc = &vcpu->arch.mmu_shadow_page_cache;
+	int start, end, i, r;
+
+	if (shadow_init_value)
+		start = kvm_mmu_memory_cache_nr_free_objects(mc);
+
+	r = kvm_mmu_topup_memory_cache(mc, PT64_ROOT_MAX_LEVEL);
+	if (r)
+		return r;
+
+	if (shadow_init_value) {
+		end = kvm_mmu_memory_cache_nr_free_objects(mc);
+		for (i = start; i < end; i++)
+			kvm_init_shadow_page(mc->objects[i]);
+	}
+	return 0;
+}
+
 static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu, bool maybe_indirect)
 {
 	int r;
@@ -752,8 +788,7 @@ static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu, bool maybe_indirect)
 				       1 + PT64_ROOT_MAX_LEVEL + PTE_PREFETCH_NUM);
 	if (r)
 		return r;
-	r = kvm_mmu_topup_memory_cache(&vcpu->arch.mmu_shadow_page_cache,
-				       PT64_ROOT_MAX_LEVEL);
+	r = mmu_topup_shadow_page_cache(vcpu);
 	if (r)
 		return r;
 	if (maybe_indirect) {
@@ -3165,7 +3200,7 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 {
 	struct kvm_mmu_page *sp;
 	int ret = RET_PF_INVALID;
-	u64 spte = 0ull;
+	u64 spte = shadow_init_value;
 	u64 *sptep = NULL;
 	uint retry_count = 0;
 
@@ -5584,7 +5619,8 @@ int kvm_mmu_create(struct kvm_vcpu *vcpu)
 	vcpu->arch.mmu_page_header_cache.kmem_cache = mmu_page_header_cache;
 	vcpu->arch.mmu_page_header_cache.gfp_zero = __GFP_ZERO;
 
-	vcpu->arch.mmu_shadow_page_cache.gfp_zero = __GFP_ZERO;
+	if (!shadow_init_value)
+		vcpu->arch.mmu_shadow_page_cache.gfp_zero = __GFP_ZERO;
 
 	vcpu->arch.mmu = &vcpu->arch.root_mmu;
 	vcpu->arch.walk_mmu = &vcpu->arch.root_mmu;
diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
index 0c76c45fdb68..bb45e71eb105 100644
--- a/arch/x86/kvm/mmu/spte.c
+++ b/arch/x86/kvm/mmu/spte.c
@@ -34,6 +34,7 @@ u64 __read_mostly shadow_mmio_access_mask;
 u64 __read_mostly shadow_present_mask;
 u64 __read_mostly shadow_me_mask;
 u64 __read_mostly shadow_acc_track_mask;
+u64 __read_mostly shadow_init_value;
 
 u64 __read_mostly shadow_nonpresent_or_rsvd_mask;
 u64 __read_mostly shadow_nonpresent_or_rsvd_lower_gfn_mask;
@@ -221,6 +222,14 @@ u64 kvm_mmu_changed_pte_notifier_make_spte(u64 old_spte, kvm_pfn_t new_pfn)
 	return new_spte;
 }
 
+void kvm_mmu_set_spte_init_value(u64 init_value)
+{
+	if (WARN_ON(!IS_ENABLED(CONFIG_X86_64) && init_value))
+		init_value = 0;
+	shadow_init_value = init_value;
+}
+EXPORT_SYMBOL_GPL(kvm_mmu_set_spte_init_value);
+
 static u8 kvm_get_shadow_phys_bits(void)
 {
 	/*
@@ -365,6 +374,7 @@ void kvm_mmu_reset_all_pte_masks(void)
 	shadow_present_mask	= PT_PRESENT_MASK;
 	shadow_acc_track_mask	= 0;
 	shadow_me_mask		= sme_me_mask;
+	shadow_init_value	= 0;
 
 	shadow_host_writable_mask = DEFAULT_SPTE_HOST_WRITEABLE;
 	shadow_mmu_writable_mask  = DEFAULT_SPTE_MMU_WRITEABLE;
diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
index 56b6dd750fb1..b53b301301dc 100644
--- a/arch/x86/kvm/mmu/spte.h
+++ b/arch/x86/kvm/mmu/spte.h
@@ -146,6 +146,8 @@ extern u64 __read_mostly shadow_mmio_access_mask;
 extern u64 __read_mostly shadow_present_mask;
 extern u64 __read_mostly shadow_me_mask;
 
+extern u64 __read_mostly shadow_init_value;
+
 /*
  * SPTEs in MMUs without A/D bits are marked with SPTE_TDP_AD_DISABLED_MASK;
  * shadow_acc_track_mask is the set of bits to be cleared in non-accessed
-- 
2.25.1