linux-kernel - [PATCH 4/7] kvm: vmx: Set IBPB when running a different VCPU

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Date:   Mon,  8 Jan 2018 19:08:42 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     jmattson@...gle.com, aliguori@...zon.com, thomas.lendacky@....com,
        dwmw@...zon.co.uk, bp@...en8.de,
        Tim Chen <tim.c.chen@...ux.intel.com>
Subject: [PATCH 4/7] kvm: vmx: Set IBPB when running a different VCPU

From: Tim Chen <tim.c.chen@...ux.intel.com>

Ensure an IBPB (Indirect branch prediction barrier) before every VCPU
switch.

Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/vmx.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index d00bcad7336e..bf127c570675 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2375,6 +2375,8 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	if (per_cpu(current_vmcs, cpu) != vmx->loaded_vmcs->vmcs) {
 		per_cpu(current_vmcs, cpu) = vmx->loaded_vmcs->vmcs;
 		vmcs_load(vmx->loaded_vmcs->vmcs);
+		if (have_spec_ctrl)
+			wrmsrl(MSR_IA32_PRED_CMD, FEATURE_SET_IBPB);
 	}
 
 	if (!already_loaded) {
@@ -4029,6 +4031,13 @@ static void free_loaded_vmcs(struct loaded_vmcs *loaded_vmcs)
 	free_vmcs(loaded_vmcs->vmcs);
 	loaded_vmcs->vmcs = NULL;
 	WARN_ON(loaded_vmcs->shadow_vmcs != NULL);
+
+	/*
+	 * The VMCS could be recycled, causing a false negative in
+	 * vmx_vcpu_load; block speculative execution.
+	 */
+	if (have_spec_ctrl)
+		wrmsrl(MSR_IA32_PRED_CMD, FEATURE_SET_IBPB);
 }
 
 static void vmx_nested_free_vmcs02(struct vcpu_vmx *vmx)
-- 
1.8.3.1