linux-kernel - [PATCH v2 06/25] KVM: VMX: Defer enabling FRED MSRs save/load until after set CPUID

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Message-ID: <20240207172646.3981-7-xin3.li@intel.com>
Date: Wed,  7 Feb 2024 09:26:26 -0800
From: Xin Li <xin3.li@...el.com>
To: linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org,
	linux-doc@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Cc: seanjc@...gle.com,
	pbonzini@...hat.com,
	corbet@....net,
	tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	x86@...nel.org,
	hpa@...or.com,
	shuah@...nel.org,
	vkuznets@...hat.com,
	peterz@...radead.org,
	ravi.v.shankar@...el.com,
	xin@...or.com
Subject: [PATCH v2 06/25] KVM: VMX: Defer enabling FRED MSRs save/load until after set CPUID

Clear FRED VM entry/exit controls when initializing a vCPU, and set
these controls only if FRED is enumerated after set CPUID.

FRED VM entry/exit controls need to be set to establish context
sufficient to support FRED event delivery immediately after VM entry
and exit.  However it is not required to save/load FRED MSRs for
a non-FRED guest, which aren't supposed to access FRED MSRs.

Signed-off-by: Xin Li <xin3.li@...el.com>
Tested-by: Shan Kang <shan.kang@...el.com>
---

Changes since v1:
* Use kvm_cpu_cap_has() instead of cpu_feature_enabled() (Chao Gao).
* Clear FRED VM entry/exit controls if FRED is not enumerated (Chao Gao).
* Use guest_can_use() to trace FRED enumeration in a vcpu (Chao Gao).
---
 arch/x86/kvm/governed_features.h |  1 +
 arch/x86/kvm/vmx/vmx.c           | 32 +++++++++++++++++++++++++++++++-
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/governed_features.h b/arch/x86/kvm/governed_features.h
index ad463b1ed4e4..507ca73e52e9 100644
--- a/arch/x86/kvm/governed_features.h
+++ b/arch/x86/kvm/governed_features.h
@@ -17,6 +17,7 @@ KVM_GOVERNED_X86_FEATURE(PFTHRESHOLD)
 KVM_GOVERNED_X86_FEATURE(VGIF)
 KVM_GOVERNED_X86_FEATURE(VNMI)
 KVM_GOVERNED_X86_FEATURE(LAM)
+KVM_GOVERNED_X86_FEATURE(FRED)
 
 #undef KVM_GOVERNED_X86_FEATURE
 #undef KVM_GOVERNED_FEATURE
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 4023474ea002..34b6676f60d8 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4402,6 +4402,9 @@ static u32 vmx_vmentry_ctrl(void)
 	if (cpu_has_perf_global_ctrl_bug())
 		vmentry_ctrl &= ~VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL;
 
+	/* Whether to load guest FRED MSRs is deferred until after set CPUID */
+	vmentry_ctrl &= ~VM_ENTRY_LOAD_IA32_FRED;
+
 	return vmentry_ctrl;
 }
 
@@ -4430,7 +4433,13 @@ static u32 vmx_vmexit_ctrl(void)
 
 static u64 vmx_secondary_vmexit_ctrl(void)
 {
-	return vmcs_config.secondary_vmexit_ctrl;
+	u64 secondary_vmexit_ctrl = vmcs_config.secondary_vmexit_ctrl;
+
+	/* Whether to save/load FRED MSRs is deferred until after set CPUID */
+	secondary_vmexit_ctrl &= ~(SECONDARY_VM_EXIT_SAVE_IA32_FRED |
+				   SECONDARY_VM_EXIT_LOAD_IA32_FRED);
+
+	return secondary_vmexit_ctrl;
 }
 
 static void vmx_refresh_apicv_exec_ctrl(struct kvm_vcpu *vcpu)
@@ -7762,10 +7771,31 @@ static void update_intel_pt_cfg(struct kvm_vcpu *vcpu)
 		vmx->pt_desc.ctl_bitmask &= ~(0xfULL << (32 + i * 4));
 }
 
+static void vmx_vcpu_config_fred_after_set_cpuid(struct kvm_vcpu *vcpu)
+{
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
+
+	kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_FRED);
+
+	if (guest_can_use(vcpu, X86_FEATURE_FRED)) {
+		vm_entry_controls_setbit(vmx, VM_ENTRY_LOAD_IA32_FRED);
+		secondary_vm_exit_controls_setbit(vmx,
+						  SECONDARY_VM_EXIT_SAVE_IA32_FRED |
+						  SECONDARY_VM_EXIT_LOAD_IA32_FRED);
+	} else {
+		vm_entry_controls_clearbit(vmx, VM_ENTRY_LOAD_IA32_FRED);
+		secondary_vm_exit_controls_clearbit(vmx,
+						    SECONDARY_VM_EXIT_SAVE_IA32_FRED |
+						    SECONDARY_VM_EXIT_LOAD_IA32_FRED);
+	}
+}
+
 static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 
+	vmx_vcpu_config_fred_after_set_cpuid(vcpu);
+
 	/*
 	 * XSAVES is effectively enabled if and only if XSAVE is also exposed
 	 * to the guest.  XSAVES depends on CR4.OSXSAVE, and CR4.OSXSAVE can be
-- 
2.43.0