linux-kernel - [PATCH 1/2] x86/kvm/hyper-v: nested_enable_evmcs() sets vmcs

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Date:   Thu, 17 Jan 2019 18:12:09 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, Liran Alon <liran.alon@...cle.com>
Subject: [PATCH 1/2] x86/kvm/hyper-v: nested_enable_evmcs() sets vmcs_version incorrectly

Commit e2e871ab2f02 ("x86/kvm/hyper-v: Introduce nested_get_evmcs_version()
helper") broke EVMCS enablement: to set vmcs_version we now call
nested_get_evmcs_version() but this function checks
enlightened_vmcs_enabled flag which is not yet set so we end up returning
zero.

Fix the issue by re-arranging things in nested_enable_evmcs().

Fixes: e2e871ab2f02 ("x86/kvm/hyper-v: Introduce nested_get_evmcs_version() helper")
Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/kvm/vmx/evmcs.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/vmx/evmcs.c b/arch/x86/kvm/vmx/evmcs.c
index 95bc2247478d..5466c6d85cf3 100644
--- a/arch/x86/kvm/vmx/evmcs.c
+++ b/arch/x86/kvm/vmx/evmcs.c
@@ -332,16 +332,17 @@ int nested_enable_evmcs(struct kvm_vcpu *vcpu,
 			uint16_t *vmcs_version)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	bool evmcs_already_enabled = vmx->nested.enlightened_vmcs_enabled;
+
+	vmx->nested.enlightened_vmcs_enabled = true;
 
 	if (vmcs_version)
 		*vmcs_version = nested_get_evmcs_version(vcpu);
 
 	/* We don't support disabling the feature for simplicity. */
-	if (vmx->nested.enlightened_vmcs_enabled)
+	if (evmcs_already_enabled)
 		return 0;
 
-	vmx->nested.enlightened_vmcs_enabled = true;
-
 	vmx->nested.msrs.pinbased_ctls_high &= ~EVMCS1_UNSUPPORTED_PINCTRL;
 	vmx->nested.msrs.entry_ctls_high &= ~EVMCS1_UNSUPPORTED_VMENTRY_CTRL;
 	vmx->nested.msrs.exit_ctls_high &= ~EVMCS1_UNSUPPORTED_VMEXIT_CTRL;
-- 
2.20.1