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Reply-To: Sean Christopherson <seanjc@google.com>
Date:   Tue,  4 May 2021 10:17:30 -0700
In-Reply-To: <20210504171734.1434054-1-seanjc@google.com>
Message-Id: <20210504171734.1434054-12-seanjc@google.com>
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Subject: [PATCH 11/15] KVM: VMX: Disable loading of TSX_CTRL MSR the more
 conventional way
From:   Sean Christopherson <seanjc@google.com>
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, Xiaoyao Li <xiaoyao.li@intel.com>,
        Reiji Watanabe <reijiw@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Tag TSX_CTRL as not needing to be loaded when RTM isn't supported in the
host.  Crushing the write mask to '0' has the same effect, but requires
more mental gymnastics to understand.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/vmx.c | 22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 4b432d2bbd06..7a53568b34fc 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1771,7 +1771,13 @@ static void setup_msrs(struct vcpu_vmx *vmx)
 			   guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDTSCP) ||
 			   guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDPID));
 
-	vmx_setup_uret_msr(vmx, MSR_IA32_TSX_CTRL, true);
+	/*
+	 * hle=0, rtm=0, tsx_ctrl=1 can be found with some combinations of new
+	 * kernel and old userspace.  If those guests run on a tsx=off host, do
+	 * allow guests to use TSX_CTRL, but don't change the value in hardware
+	 * so that TSX remains always disabled.
+	 */
+	vmx_setup_uret_msr(vmx, MSR_IA32_TSX_CTRL, boot_cpu_has(X86_FEATURE_RTM));
 
 	if (cpu_has_vmx_msr_bitmap())
 		vmx_update_msr_bitmap(&vmx->vcpu);
@@ -6919,23 +6925,15 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu)
 		vmx->guest_uret_msrs[i].data = 0;
 		vmx->guest_uret_msrs[i].mask = -1ull;
 	}
-	tsx_ctrl = vmx_find_uret_msr(vmx, MSR_IA32_TSX_CTRL);
-	if (tsx_ctrl) {
+	if (boot_cpu_has(X86_FEATURE_RTM)) {
 		/*
 		 * TSX_CTRL_CPUID_CLEAR is handled in the CPUID interception.
 		 * Keep the host value unchanged to avoid changing CPUID bits
 		 * under the host kernel's feet.
-		 *
-		 * hle=0, rtm=0, tsx_ctrl=1 can be found with some combinations
-		 * of new kernel and old userspace.  If those guests run on a
-		 * tsx=off host, do allow guests to use TSX_CTRL, but do not
-		 * change the value on the host so that TSX remains always
-		 * disabled.
 		 */
-		if (boot_cpu_has(X86_FEATURE_RTM))
+		tsx_ctrl = vmx_find_uret_msr(vmx, MSR_IA32_TSX_CTRL);
+		if (tsx_ctrl)
 			vmx->guest_uret_msrs[i].mask = ~(u64)TSX_CTRL_CPUID_CLEAR;
-		else
-			vmx->guest_uret_msrs[i].mask = 0;
 	}
 
 	err = alloc_loaded_vmcs(&vmx->vmcs01);
-- 
2.31.1.527.g47e6f16901-goog