Re: [PATCH] KVM: nVMX: INVPCID support

From: Paolo Bonzini
Date: Tue Aug 01 2017 - 07:35:43 EST

On 01/08/2017 13:18, David Hildenbrand wrote:
>>> Can't we rewrite that a little bit, avoiding that "best" handling
>>> (introducing guest_cpuid_disable_invpcid() and guest_cpuid_has_invpcid())
>>> bool invpcid_enabled = guest_cpuid_has_pcid(vcpu) &&
>>> guest_cpuid_has_invpcid();
>>> if (!invpcid_enabled) {
>>> secondary_exec_ctl &= ~SECONDARY_EXEC_ENABLE_INVPCID;
>>> /* make sure there is no no INVPCID without PCID */
>>> guest_cpuid_disable_invpcid(vcpu);
>>> }
>> I don't know... if you need a comment, it means the different structure
>> of the code doesn't spare many doubts from the reader. And the code
>> doesn't become much simpler since you have to handle "nested" anyway.
>> What I tried to do was to mimic as much as possible the rdtscp case, but
>> it cannot be exactly the same due to the interaction between PCID and
> It's more about the handling of best here, which can be avoided quite
> easily as I showed (by encapsulating how cpuids are looked up/modified).

Yeah, I don't like either option. :) Luckily there is a second maintainer!