linux-kernel - [PATCH 7/9] x86/kvm/nVMX: introduce scache for kvm_init_shadow_ept

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Message-Id: <20180802100132.5249-8-vkuznets@redhat.com>
Date:   Thu,  2 Aug 2018 12:01:30 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, Jim Mattson <jmattson@...gle.com>,
        Liran Alon <liran.alon@...cle.com>
Subject: [PATCH 7/9] x86/kvm/nVMX: introduce scache for kvm_init_shadow_ept_mmu

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.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/include/asm/kvm_host.h | 14 +++++++++++
 arch/x86/kvm/mmu.c              | 51 ++++++++++++++++++++++++++++++-----------
 2 files changed, 52 insertions(+), 13 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 830166ab4d59..d44668dcf655 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -272,8 +272,22 @@ union kvm_mmu_page_role {
 	};
 };
 
+/*
+ * This structure complements kvm_mmu_page_role caching everything needed for
+ * MMU configuration. If nothing in both these structures changed, MMU
+ * re-configuration can be skipped. @valid bit is set on first usage so we don't
+ * treat all-zero structure as valid data.
+ */
 union kvm_mmu_scache {
 	unsigned int word;
+	struct {
+		unsigned int valid:1;
+		unsigned int execonly:1;
+		unsigned int cr4_pse:1;
+		unsigned int cr4_pke:1;
+		unsigned int cr4_smap:1;
+		unsigned int cr4_smep:1;
+	};
 };
 
 union kvm_mmu_role {
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index c538e47e471b..c46f875bf937 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -4678,6 +4678,24 @@ static void paging32E_init_context(struct kvm_vcpu *vcpu,
 	paging64_init_context_common(vcpu, context, PT32E_ROOT_LEVEL);
 }
 
+static union kvm_mmu_role
+kvm_calc_mmu_role_common(struct kvm_vcpu *vcpu)
+{
+	union kvm_mmu_role role = {0};
+
+	role.base_role.access = ACC_ALL;
+	role.base_role.cr0_wp = is_write_protection(vcpu);
+
+	role.scache.cr4_smep = kvm_read_cr4_bits(vcpu, X86_CR4_SMEP) != 0;
+	role.scache.cr4_smap = kvm_read_cr4_bits(vcpu, X86_CR4_SMAP) != 0;
+	role.scache.cr4_pse = !!is_pse(vcpu);
+	role.scache.cr4_pke = kvm_read_cr4_bits(vcpu, X86_CR4_PKE) != 0;
+
+	role.scache.valid = 1;
+
+	return role;
+}
+
 static union kvm_mmu_page_role
 kvm_calc_tdp_mmu_root_page_role(struct kvm_vcpu *vcpu)
 {
@@ -4784,16 +4802,18 @@ void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(kvm_init_shadow_mmu);
 
-static union kvm_mmu_page_role
-kvm_calc_shadow_ept_root_page_role(struct kvm_vcpu *vcpu, bool accessed_dirty)
+static union kvm_mmu_role
+kvm_calc_shadow_ept_root_page_role(struct kvm_vcpu *vcpu, bool accessed_dirty,
+				   bool execonly)
 {
-	union kvm_mmu_page_role role = vcpu->arch.mmu->mmu_role.base_role;
+	union kvm_mmu_role role = kvm_calc_mmu_role_common(vcpu);
 
-	role.level = PT64_ROOT_4LEVEL;
-	role.direct = false;
-	role.ad_disabled = !accessed_dirty;
-	role.guest_mode = true;
-	role.access = ACC_ALL;
+	role.base_role.level = PT64_ROOT_4LEVEL;
+	role.base_role.direct = false;
+	role.base_role.ad_disabled = !accessed_dirty;
+	role.base_role.guest_mode = true;
+
+	role.scache.execonly = execonly;
 
 	return role;
 }
@@ -4802,10 +4822,16 @@ void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly,
 			     bool accessed_dirty, gpa_t new_eptp)
 {
 	struct kvm_mmu *context = vcpu->arch.mmu;
-	union kvm_mmu_page_role root_page_role =
-		kvm_calc_shadow_ept_root_page_role(vcpu, accessed_dirty);
+	union kvm_mmu_role new_role =
+		kvm_calc_shadow_ept_root_page_role(vcpu, accessed_dirty,
+						   execonly);
+
+	__kvm_mmu_new_cr3(vcpu, new_eptp, new_role.base_role, false);
+
+	new_role.base_role.word &= mmu_base_role_mask.word;
+	if (new_role.as_u64 == context->mmu_role.as_u64)
+		return;
 
-	__kvm_mmu_new_cr3(vcpu, new_eptp, root_page_role, false);
 	context->shadow_root_level = PT64_ROOT_4LEVEL;
 
 	context->nx = true;
@@ -4817,8 +4843,7 @@ void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly,
 	context->update_pte = ept_update_pte;
 	context->root_level = PT64_ROOT_4LEVEL;
 	context->direct_map = false;
-	context->mmu_role.base_role.word =
-		root_page_role.word & mmu_base_role_mask.word;
+	context->mmu_role.as_u64 = new_role.as_u64;
 	context->get_pdptr = kvm_pdptr_read;
 
 	update_permission_bitmask(vcpu, context, true);
-- 
2.14.4