[PATCH RFC 6/7] x86/kvm/nVMX: introduce scache for kvm_init_shadow_ept_mmu

[Vitaly Kuznetsov]

MMU re-initialization is expensive, in particular,
update_permission_bitmask() and update_pkru_bitmask() are.

Cache the data used to setup shadow EPT MMU and avoid full re-init when
it is unchanged.

kvm_mmu_free_roots() can be dropped from nested_ept_init_mmu_context()
as we always do kvm_mmu_reset_context() in nested_vmx_load_cr3().

Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h | 15 +++++++++++++
 arch/x86/kvm/mmu.c              | 50 ++++++++++++++++++++++++++++++++++++++++-
 arch/x86/kvm/vmx.c              |  5 +++--
 3 files changed, 67 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 2c0b493e09f7..fa73cf13c4d0 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -325,6 +325,19 @@ struct rsvd_bits_validate {
 	u64 bad_mt_xwr;
 };
 
+/* Source data used to setup MMU */
+struct kvm_mmu_sdata_cache {
+	unsigned int valid:1;
+	unsigned int ept_ad:1;
+	unsigned int execonly:1;
+	unsigned int cr0_wp:1;
+	unsigned int cr4_pae:1;
+	unsigned int cr4_pse:1;
+	unsigned int cr4_pke:1;
+	unsigned int cr4_smap:1;
+	unsigned int cr4_smep:1;
+};
+
 /*
  * x86 supports 4 paging modes (5-level 64-bit, 4-level 64-bit, 3-level 32-bit,
  * and 2-level 32-bit).  The kvm_mmu structure abstracts the details of the
@@ -387,6 +400,8 @@ struct kvm_mmu {
 	bool nx;
 
 	u64 pdptrs[4]; /* pae */
+
+	struct kvm_mmu_sdata_cache scache;
 };
 
 enum pmc_type {
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index fb6652643b15..eed1773453cd 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -4548,12 +4548,60 @@ void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(kvm_init_shadow_mmu);
 
+static inline bool shadow_ept_mmu_update_needed(struct kvm_vcpu *vcpu,
+					bool execonly, bool accessed_dirty)
+{
+	struct kvm_mmu *context = vcpu->arch.mmu;
+	bool cr4_smep = kvm_read_cr4_bits(vcpu, X86_CR4_SMEP) != 0;
+	bool cr4_smap = kvm_read_cr4_bits(vcpu, X86_CR4_SMAP) != 0;
+	bool cr4_pke = kvm_read_cr4_bits(vcpu, X86_CR4_PKE) != 0;
+	bool cr0_wp = is_write_protection(vcpu);
+	bool cr4_pse = is_pse(vcpu);
+	bool res = false;
+
+	if (!context->scache.valid) {
+		res = true;
+		context->scache.valid = 1;
+	}
+	if (context->scache.ept_ad != accessed_dirty) {
+		context->scache.ept_ad = accessed_dirty;
+		res = true;
+	}
+	if (context->scache.execonly != execonly) {
+		res = true;
+		context->scache.execonly = execonly;
+	}
+	if (context->scache.cr4_smap != cr4_smap) {
+		res = true;
+		context->scache.cr4_smap = cr4_smap;
+	}
+	if (context->scache.cr4_smep != cr4_smep) {
+		res = true;
+		context->scache.cr4_smep = cr4_smep;
+	}
+	if (context->scache.cr4_pse != cr4_pse) {
+		res = true;
+		context->scache.cr4_pse = cr4_pse;
+	}
+	if (context->scache.cr4_pke != cr4_pke) {
+		res = true;
+		context->scache.cr4_pke = cr4_pke;
+	}
+	if (context->scache.cr0_wp != cr0_wp) {
+		res = true;
+		context->scache.cr0_wp = cr0_wp;
+	}
+
+	return res;
+}
+
 void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly,
 			     bool accessed_dirty)
 {
 	struct kvm_mmu *context = vcpu->arch.mmu;
 
-	MMU_WARN_ON(VALID_PAGE(context->root_hpa));
+	if (!shadow_ept_mmu_update_needed(vcpu, execonly, accessed_dirty))
+		return;
 
 	context->shadow_root_level = PT64_ROOT_4LEVEL;
 
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 5feb52991065..3467665a75d5 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -10577,12 +10577,13 @@ static unsigned long nested_ept_get_cr3(struct kvm_vcpu *vcpu)
 
 static int nested_ept_init_mmu_context(struct kvm_vcpu *vcpu)
 {
+	unsigned long cr3 = nested_ept_get_cr3(vcpu);
+
 	WARN_ON(mmu_is_nested(vcpu));
-	if (!valid_ept_address(vcpu, nested_ept_get_cr3(vcpu)))
+	if (!valid_ept_address(vcpu, cr3))
 		return 1;
 
 	vcpu->arch.mmu = &vcpu->arch.guest_mmu;
-	kvm_mmu_free_roots(vcpu, &vcpu->arch.guest_mmu);
 
 	kvm_init_shadow_ept_mmu(vcpu,
 			to_vmx(vcpu)->nested.msrs.ept_caps &
-- 
2.14.4