linux-kernel - [RFC PATCH v3 03/10] KVM: nVMX: Enable SPEC

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Date: Wed, 10 Apr 2024 22:34:31 +0800
From: Chao Gao <chao.gao@...el.com>
To: kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: daniel.sneddon@...ux.intel.com,
	pawan.kumar.gupta@...ux.intel.com,
	Chao Gao <chao.gao@...el.com>,
	Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [RFC PATCH v3 03/10] KVM: nVMX: Enable SPEC_CTRL virtualizaton for vmcs02

to prevent nested guests from changing the SPEC_CTRL bits that userspace
doesn't allow a guest to change.

Propagate tertiary vm-exec controls from vmcs01 to vmcs02 and program
the mask of SPEC_CTRL MSRs as the userspace VMM requested.

With SPEC_CTRL virtualization enabled, guest will read from the shadow
value in VMCS. To ensure consistent view across nested VMX transitions,
propagate the shadow value between vmcs01 and vmcs02.

Signed-off-by: Chao Gao <chao.gao@...el.com>
---
 arch/x86/kvm/vmx/nested.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index d05ddf751491..174790b2ffbc 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2381,6 +2381,20 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct loaded_vmcs *vmcs0
 		secondary_exec_controls_set(vmx, exec_control);
 	}
 
+	/*
+	 * TERTIARY EXEC CONTROLS
+	 */
+	if (cpu_has_tertiary_exec_ctrls()) {
+		exec_control = __tertiary_exec_controls_get(vmcs01);
+
+		exec_control &= TERTIARY_EXEC_SPEC_CTRL_SHADOW;
+		if (exec_control & TERTIARY_EXEC_SPEC_CTRL_SHADOW)
+			vmcs_write64(IA32_SPEC_CTRL_MASK,
+				     vmx->vcpu.kvm->arch.force_spec_ctrl_mask);
+
+		tertiary_exec_controls_set(vmx, exec_control);
+	}
+
 	/*
 	 * ENTRY CONTROLS
 	 *
@@ -2625,6 +2639,19 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
 	if (kvm_caps.has_tsc_control)
 		vmcs_write64(TSC_MULTIPLIER, vcpu->arch.tsc_scaling_ratio);
 
+	/*
+	 * L2 after nested VM-entry should observe the same value of
+	 * IA32_SPEC_CTRL MSR as L1 unless:
+	 *	a. L1 loads IA32_SPEC_CTRL via MSR-load area.
+	 *	b. L1 enables IA32_SPEC_CTRL virtualization. this cannot
+	 *	   happen since KVM doesn't expose this feature to L1.
+	 *
+	 * Propagate spec_ctrl_shadow (the value guest will get via RDMSR)
+	 * to vmcs02. Later nested_vmx_load_msr() will take care of case a.
+	 */
+	if (vmx->nested.nested_run_pending && cpu_has_spec_ctrl_shadow())
+		vmcs_write64(IA32_SPEC_CTRL_SHADOW, vmx->spec_ctrl_shadow);
+
 	nested_vmx_transition_tlb_flush(vcpu, vmcs12, true);
 
 	if (nested_cpu_has_ept(vmcs12))
@@ -4883,6 +4910,9 @@ void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 vm_exit_reason,
 		vmx_update_cpu_dirty_logging(vcpu);
 	}
 
+	if (cpu_has_spec_ctrl_shadow())
+		vmcs_write64(IA32_SPEC_CTRL_SHADOW, vmx->spec_ctrl_shadow);
+
 	/* Unpin physical memory we referred to in vmcs02 */
 	kvm_vcpu_unmap(vcpu, &vmx->nested.apic_access_page_map, false);
 	kvm_vcpu_unmap(vcpu, &vmx->nested.virtual_apic_map, true);
-- 
2.39.3