linux-kernel - [PATCH v6 2/7] KVM: VMX: Add proper cache tracking for PKRS

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Date:   Mon, 21 Feb 2022 16:08:35 +0800
From:   Chenyi Qiang <chenyi.qiang@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     Chenyi Qiang <chenyi.qiang@...el.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v6 2/7] KVM: VMX: Add proper cache tracking for PKRS

Add PKRS caching into the standard register caching mechanism in order
to take advantage of the availability checks provided by regs_avail.

This is because vcpu->arch.pkrs will be rarely acceesed by KVM, only in
the case of host userspace MSR reads and GVA->GPA translation in
following patches. It is unnecessary to keep it up-to-date at all times.

Signed-off-by: Chenyi Qiang <chenyi.qiang@...el.com>
---
 arch/x86/include/asm/kvm_host.h |  2 ++
 arch/x86/kvm/kvm_cache_regs.h   |  7 +++++++
 arch/x86/kvm/vmx/vmx.c          | 11 +++++++++++
 arch/x86/kvm/vmx/vmx.h          |  3 ++-
 4 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 1384517d7709..75940aeb5f67 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -177,6 +177,7 @@ enum kvm_reg {
 	VCPU_EXREG_SEGMENTS,
 	VCPU_EXREG_EXIT_INFO_1,
 	VCPU_EXREG_EXIT_INFO_2,
+	VCPU_EXREG_PKRS,
 };
 
 enum {
@@ -632,6 +633,7 @@ struct kvm_vcpu_arch {
 	unsigned long cr8;
 	u32 host_pkru;
 	u32 pkru;
+	u32 pkrs;
 	u32 hflags;
 	u64 efer;
 	u64 apic_base;
diff --git a/arch/x86/kvm/kvm_cache_regs.h b/arch/x86/kvm/kvm_cache_regs.h
index 3febc342360c..2b2540ca584f 100644
--- a/arch/x86/kvm/kvm_cache_regs.h
+++ b/arch/x86/kvm/kvm_cache_regs.h
@@ -177,6 +177,13 @@ static inline u64 kvm_read_edx_eax(struct kvm_vcpu *vcpu)
 		| ((u64)(kvm_rdx_read(vcpu) & -1u) << 32);
 }
 
+static inline u32 kvm_read_pkrs(struct kvm_vcpu *vcpu)
+{
+	if (!kvm_register_is_available(vcpu, VCPU_EXREG_PKRS))
+		static_call(kvm_x86_cache_reg)(vcpu, VCPU_EXREG_PKRS);
+	return vcpu->arch.pkrs;
+}
+
 static inline void enter_guest_mode(struct kvm_vcpu *vcpu)
 {
 	vcpu->arch.hflags |= HF_GUEST_MASK;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 4ac676066d60..0496afe786fa 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2269,6 +2269,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 static void vmx_cache_reg(struct kvm_vcpu *vcpu, enum kvm_reg reg)
 {
 	unsigned long guest_owned_bits;
+	u64 ia32_pkrs;
 
 	kvm_register_mark_available(vcpu, reg);
 
@@ -2303,6 +2304,16 @@ static void vmx_cache_reg(struct kvm_vcpu *vcpu, enum kvm_reg reg)
 		vcpu->arch.cr4 &= ~guest_owned_bits;
 		vcpu->arch.cr4 |= vmcs_readl(GUEST_CR4) & guest_owned_bits;
 		break;
+	case VCPU_EXREG_PKRS:
+		/*
+		 * The high 32 bits of PKRS are reserved and attempting to write
+		 * non-zero value will cause #GP. KVM intentionally drops those
+		 * bits.
+		 */
+		ia32_pkrs = vmcs_read64(GUEST_IA32_PKRS);
+		WARN_ON_ONCE(ia32_pkrs >> 32);
+		vcpu->arch.pkrs = ia32_pkrs;
+		break;
 	default:
 		KVM_BUG_ON(1, vcpu->kvm);
 		break;
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 7f2c82e7f38f..da5e95a6694c 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -500,7 +500,8 @@ BUILD_CONTROLS_SHADOW(secondary_exec, SECONDARY_VM_EXEC_CONTROL)
 				(1 << VCPU_EXREG_CR3) |         \
 				(1 << VCPU_EXREG_CR4) |         \
 				(1 << VCPU_EXREG_EXIT_INFO_1) | \
-				(1 << VCPU_EXREG_EXIT_INFO_2))
+				(1 << VCPU_EXREG_EXIT_INFO_2) | \
+				(1 << VCPU_EXREG_PKRS))
 
 static inline struct kvm_vmx *to_kvm_vmx(struct kvm *kvm)
 {
-- 
2.17.1