From c532f2903b69b775d27016511fbe29a14a098f95 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Thu, 20 Jan 2022 01:07:14 +0000 Subject: [PATCH] KVM: SVM: Explicitly require DECODEASSISTS to enable SEV support Add a sanity check on DECODEASSIST being support if SEV is supported, as KVM cannot read guest private memory and thus relies on the CPU to provide the instruction byte stream on #NPF for emulation. The intent of the check is to document the dependency, it should never fail in practice as producing hardware that supports SEV but not DECODEASSISTS would be non-sensical. Signed-off-by: Sean Christopherson Reviewed-by: Liam Merwick Message-Id: <20220120010719.711476-5-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/svm/sev.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index 6a22798eaaee..17b53457d866 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -2100,8 +2100,13 @@ void __init sev_hardware_setup(void) if (!sev_enabled || !npt_enabled) goto out; - /* Does the CPU support SEV? */ - if (!boot_cpu_has(X86_FEATURE_SEV)) + /* + * SEV must obviously be supported in hardware. Sanity check that the + * CPU supports decode assists, which is mandatory for SEV guests to + * support instruction emulation. + */ + if (!boot_cpu_has(X86_FEATURE_SEV) || + WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_DECODEASSISTS))) goto out; /* Retrieve SEV CPUID information */ -- 2.11.0