KVM: x86/mmu: Replace hardcoded value 0 for the initial value for SPTE

The TDX support will need the "suppress #VE" bit (bit 63) set as the
initial value for SPTE.  To reduce code change size, introduce a new macro
SHADOW_NONPRESENT_VALUE for the initial value for the shadow page table
entry (SPTE) and replace hard-coded value 0 for it.  Initialize shadow page
tables with their value.

The plan is to unconditionally set the "suppress #VE" bit for both AMD and
Intel as: 1) AMD hardware uses the bit 63 as NX for present SPTE and
ignored for non-present SPTE; 2) for conventional VMX guests, KVM never
enables the "EPT-violation #VE" in VMCS control and "suppress #VE" bit is
ignored by hardware.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Message-Id: <acdf09bf60cad12c495005bf3495c54f6b3069c9.1705965635.git.isaku.yamahata@intel.com>
[Remove unnecessary CONFIG_X86_64 check. - Paolo]
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: sean-jc

arch/x86/kvm/mmu/mmu.c

@@ -567,9 +567,9 @@ static u64 mmu_spte_clear_track_bits(struct kvm *kvm, u64 *sptep)
 
 	if (!is_shadow_present_pte(old_spte) ||
 	    !spte_has_volatile_bits(old_spte))
-		__update_clear_spte_fast(sptep, 0ull);
+		__update_clear_spte_fast(sptep, SHADOW_NONPRESENT_VALUE);
 	else
-		old_spte = __update_clear_spte_slow(sptep, 0ull);
+		old_spte = __update_clear_spte_slow(sptep, SHADOW_NONPRESENT_VALUE);
 
 	if (!is_shadow_present_pte(old_spte))
 		return old_spte;
@@ -603,7 +603,7 @@ static u64 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_NONPRESENT_VALUE);
 }
 
 static u64 mmu_spte_get_lockless(u64 *sptep)
@@ -1897,7 +1897,8 @@ static bool kvm_sync_page_check(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
 
 static int kvm_sync_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, int i)
 {
-	if (!sp->spt[i])
+	/* sp->spt[i] has initial value of shadow page table allocation */
+	if (sp->spt[i] == SHADOW_NONPRESENT_VALUE)
 		return 0;
 
 	return vcpu->arch.mmu->sync_spte(vcpu, sp, i);
@@ -6120,7 +6121,10 @@ 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;
+	vcpu->arch.mmu_shadow_page_cache.init_value =
+		SHADOW_NONPRESENT_VALUE;
+	if (!vcpu->arch.mmu_shadow_page_cache.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;

arch/x86/kvm/mmu/paging_tmpl.h

@@ -911,7 +911,7 @@ static int FNAME(sync_spte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, int
 	gpa_t pte_gpa;
 	gfn_t gfn;
 
-	if (WARN_ON_ONCE(!sp->spt[i]))
+	if (WARN_ON_ONCE(sp->spt[i] == SHADOW_NONPRESENT_VALUE))
 		return 0;
 
 	first_pte_gpa = FNAME(get_level1_sp_gpa)(sp);

arch/x86/kvm/mmu/spte.h

@@ -149,6 +149,8 @@ static_assert(MMIO_SPTE_GEN_LOW_BITS == 8 && MMIO_SPTE_GEN_HIGH_BITS == 11);
 
 #define MMIO_SPTE_GEN_MASK		GENMASK_ULL(MMIO_SPTE_GEN_LOW_BITS + MMIO_SPTE_GEN_HIGH_BITS - 1, 0)
 
+#define SHADOW_NONPRESENT_VALUE	0ULL
+
 extern u64 __read_mostly shadow_host_writable_mask;
 extern u64 __read_mostly shadow_mmu_writable_mask;
 extern u64 __read_mostly shadow_nx_mask;
@@ -194,7 +196,7 @@ extern u64 __read_mostly shadow_nonpresent_or_rsvd_mask;
  *
  * Only used by the TDP MMU.
  */
-#define REMOVED_SPTE	0x5a0ULL
+#define REMOVED_SPTE	(SHADOW_NONPRESENT_VALUE | 0x5a0ULL)
 
 /* Removed SPTEs must not be misconstrued as shadow present PTEs. */
 static_assert(!(REMOVED_SPTE & SPTE_MMU_PRESENT_MASK));

arch/x86/kvm/mmu/tdp_mmu.c

@@ -603,7 +603,7 @@ static inline int tdp_mmu_zap_spte_atomic(struct kvm *kvm,
 	 * here since the SPTE is going from non-present to non-present.  Use
 	 * the raw write helper to avoid an unnecessary check on volatile bits.
 	 */
-	__kvm_tdp_mmu_write_spte(iter->sptep, 0);
+	__kvm_tdp_mmu_write_spte(iter->sptep, SHADOW_NONPRESENT_VALUE);
 
 	return 0;
 }
@@ -740,8 +740,8 @@ static void __tdp_mmu_zap_root(struct kvm *kvm, struct kvm_mmu_page *root,
 			continue;
 
 		if (!shared)
-			tdp_mmu_iter_set_spte(kvm, &iter, 0);
-		else if (tdp_mmu_set_spte_atomic(kvm, &iter, 0))
+			tdp_mmu_iter_set_spte(kvm, &iter, SHADOW_NONPRESENT_VALUE);
+		else if (tdp_mmu_set_spte_atomic(kvm, &iter, SHADOW_NONPRESENT_VALUE))
 			goto retry;
 	}
 }
@@ -808,8 +808,8 @@ bool kvm_tdp_mmu_zap_sp(struct kvm *kvm, struct kvm_mmu_page *sp)
 	if (WARN_ON_ONCE(!is_shadow_present_pte(old_spte)))
 		return false;
 
-	tdp_mmu_set_spte(kvm, kvm_mmu_page_as_id(sp), sp->ptep, old_spte, 0,
-			 sp->gfn, sp->role.level + 1);
+	tdp_mmu_set_spte(kvm, kvm_mmu_page_as_id(sp), sp->ptep, old_spte,
+			 SHADOW_NONPRESENT_VALUE, sp->gfn, sp->role.level + 1);
 
 	return true;
 }
@@ -843,7 +843,7 @@ static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct kvm_mmu_page *root,
 		    !is_last_spte(iter.old_spte, iter.level))
 			continue;
 
-		tdp_mmu_iter_set_spte(kvm, &iter, 0);
+		tdp_mmu_iter_set_spte(kvm, &iter, SHADOW_NONPRESENT_VALUE);
 
 		/*
 		 * Zappings SPTEs in invalid roots doesn't require a TLB flush,