From: Sean Christopherson seanjc@google.com
[ Upstream commit c532f2903b69b775d27016511fbe29a14a098f95 ]
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 seanjc@google.com Reviewed-by: Liam Merwick liam.merwick@oracle.com Message-Id: 20220120010719.711476-5-seanjc@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 134c4ea5e6ad8..d006eeb1d0321 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -1887,8 +1887,13 @@ 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 */