linux-kernel - [PATCH v2] KVM: VMX: Set VMENTER_L1D_FLUSH_NOT_REQUIRED if !X86_BUG

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Date:   Fri, 27 Sep 2019 18:05:16 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     bp@...en8.de, Waiman Long <longman@...hat.com>
Subject: [PATCH v2] KVM: VMX: Set VMENTER_L1D_FLUSH_NOT_REQUIRED if !X86_BUG_L1TF

From: Waiman Long <longman@...hat.com>

The l1tf_vmx_mitigation is only set to VMENTER_L1D_FLUSH_NOT_REQUIRED
when the ARCH_CAPABILITIES MSR indicates that L1D flush is not required.
However, if the CPU is not affected by L1TF, l1tf_vmx_mitigation will
still be set to VMENTER_L1D_FLUSH_AUTO. This is certainly not the best
option for a !X86_BUG_L1TF CPU.

So force l1tf_vmx_mitigation to VMENTER_L1D_FLUSH_NOT_REQUIRED to make it
more explicit in case users are checking the vmentry_l1d_flush parameter.

Signed-off-by: Waiman Long <longman@...hat.com>
[Patch rewritten accoring to Borislav Petkov's suggestion. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/vmx/vmx.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index d4575ffb3cec..e7970a2e8eae 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -209,6 +209,11 @@ static int vmx_setup_l1d_flush(enum vmx_l1d_flush_state l1tf)
 	struct page *page;
 	unsigned int i;
 
+	if (!boot_cpu_has_bug(X86_BUG_L1TF)) {
+		l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_NOT_REQUIRED;
+		return 0;
+	}
+
 	if (!enable_ept) {
 		l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_EPT_DISABLED;
 		return 0;
@@ -7995,12 +8000,10 @@ static int __init vmx_init(void)
 	 * contain 'auto' which will be turned into the default 'cond'
 	 * mitigation mode.
 	 */
-	if (boot_cpu_has(X86_BUG_L1TF)) {
-		r = vmx_setup_l1d_flush(vmentry_l1d_flush_param);
-		if (r) {
-			vmx_exit();
-			return r;
-		}
+	r = vmx_setup_l1d_flush(vmentry_l1d_flush_param);
+	if (r) {
+		vmx_exit();
+		return r;
 	}
 
 #ifdef CONFIG_KEXEC_CORE
-- 
1.8.3.1