linux-kernel - [PATCH 2/2] kvm/x86: don't expose MSR_IA32_UMWAIT

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Message-Id: <20200520160740.6144-3-mlevitsk@redhat.com>
Date:   Wed, 20 May 2020 19:07:40 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH 2/2] kvm/x86: don't expose MSR_IA32_UMWAIT_CONTROL unconditionally

This msr is only available when the host supports WAITPKG feature.

This breaks a nested guest, if the L1 hypervisor is set to ignore
unknown msrs, because the only other safety check that the
kernel does is that it attempts to read the msr and
rejects it if it gets an exception.

Fixes: 6e3ba4abce KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/x86.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fe3a24fd6b263..9c507b32b1b77 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5314,6 +5314,10 @@ static void kvm_init_msr_list(void)
 			if (msrs_to_save_all[i] - MSR_ARCH_PERFMON_EVENTSEL0 >=
 			    min(INTEL_PMC_MAX_GENERIC, x86_pmu.num_counters_gp))
 				continue;
+			break;
+		case MSR_IA32_UMWAIT_CONTROL:
+			if (!kvm_cpu_cap_has(X86_FEATURE_WAITPKG))
+				continue;
 		default:
 			break;
 		}
-- 
2.26.2