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Subject[PATCH 4/8] kvm: vmx: Set IBPB when running a different VCPU
Date
From: Tim Chen <tim.c.chen@linux.intel.com>

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

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Reviewed-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.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 ef603692aa98..49b4a2d61603 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, PRED_CMD_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, PRED_CMD_IBPB);
}

static void vmx_nested_free_vmcs02(struct vcpu_vmx *vmx)
--
1.8.3.1

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