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KVM: SVM: Explicitly require DECODEASSISTS to enable SEV support

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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>
This commit is contained in:
Sean Christopherson 2022-01-20 01:07:14 +00:00 committed by Paolo Bonzini
parent 0b0be065b7
commit c532f2903b
1 changed files with 7 additions and 2 deletions
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9
arch/x86/kvm/svm/sev.c
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@ -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 */