linux-kernel - [PATCH v3 3/4] KVM: SVM: Don't advertise Bus Lock Detect to guest if SVM support is missing

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Message-ID: <20240806125442.1603-4-ravi.bangoria@amd.com>
Date: Tue, 6 Aug 2024 12:54:41 +0000
From: Ravi Bangoria <ravi.bangoria@....com>
To: <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>, <seanjc@...gle.com>, <pbonzini@...hat.com>,
	<thomas.lendacky@....com>, <jmattson@...gle.com>
CC: <ravi.bangoria@....com>, <hpa@...or.com>, <rmk+kernel@...linux.org.uk>,
	<peterz@...radead.org>, <james.morse@....com>, <lukas.bulwahn@...il.com>,
	<arjan@...ux.intel.com>, <j.granados@...sung.com>, <sibs@...natelecom.cn>,
	<nik.borisov@...e.com>, <michael.roth@....com>, <nikunj.dadhania@....com>,
	<babu.moger@....com>, <x86@...nel.org>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <santosh.shukla@....com>,
	<ananth.narayan@....com>, <sandipan.das@....com>, <manali.shukla@....com>
Subject: [PATCH v3 3/4] KVM: SVM: Don't advertise Bus Lock Detect to guest if SVM support is missing

If host supports Bus Lock Detect, KVM advertises it to guests even if
SVM support is absent. Additionally, guest wouldn't be able to use it
despite guest CPUID bit being set. Fix it by unconditionally clearing
the feature bit in KVM cpu capability.

Reported-by: Jim Mattson <jmattson@...gle.com>
Closes: https://lore.kernel.org/r/CALMp9eRet6+v8Y1Q-i6mqPm4hUow_kJNhmVHfOV8tMfuSS=tVg@mail.gmail.com
Fixes: 76ea438b4afc ("KVM: X86: Expose bus lock debug exception to guest")
Cc: stable@...r.kernel.org
Signed-off-by: Ravi Bangoria <ravi.bangoria@....com>
Reviewed-by: Jim Mattson <jmattson@...gle.com>
---
 arch/x86/kvm/svm/svm.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index c115d26844f7..85631112c872 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -5223,6 +5223,9 @@ static __init void svm_set_cpu_caps(void)
 
 	/* CPUID 0x8000001F (SME/SEV features) */
 	sev_set_cpu_caps();
+
+	/* Don't advertise Bus Lock Detect to guest if SVM support is absent */
+	kvm_cpu_cap_clear(X86_FEATURE_BUS_LOCK_DETECT);
 }
 
 static __init int svm_hardware_setup(void)
-- 
2.34.1