Re: [PATCH] KVM: x86: add hint to skip hidden rdpkru under kvm_load_host_xsave_state

[Dave Hansen]

On 5/17/21 10:49 AM, Andy Lutomirski wrote:
>> The least awful solution would be to have the NMI handler restore
>> the host's PKRU.  The NMI handler would need to save/restore the
>> register, a la CR2, but the whole thing could be optimized to run
>> if and only if the NMI lands in the window where the guest's PKRU
>> is loaded.
> 
> Or set a flag causing nmi_uaccess_ok() to return false.

Oh, that doesn't sound too bad.  The VMENTER/EXIT paths are also
essentially a context switch.

Will widening the window where nmi_uaccess_okay()==false anger any of
the perf folks?  It looks like perf knows how to handle it nicely.