Messages in this thread | | | Subject | Re: [PATCH] kvm: x86: Use KVM CPU capabilities to determine CR4 reserved bits | From | Xiaoyao Li <> | Date | Mon, 18 May 2020 12:52:30 +0800 |
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On 5/6/2020 5:44 PM, Paolo Bonzini wrote: > Using CPUID data can be useful for the processor compatibility > check, but that's it. Using it to compute guest-reserved bits > can have both false positives (such as LA57 and UMIP which we > are already handling) and false negatives:
> in particular, with > this patch we don't allow anymore a KVM guest to set CR4.PKE > when CR4.PKE is clear on the host.
A common question about whether a feature can be exposed to guest:
Given a feature, there is a CPUID bit to enumerate it, and a CR4 bit to turn it on/off. Whether the feature can be exposed to guest only depends on host CR4 setting? I.e., if CPUID bit is not cleared in cpu_data in host but host kernel doesn't set the corresponding CR4 bit to turn it on, we cannot expose the feature to guest. right?
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