linux-kernel - Re: [PATCH] KVM: nVMX: INVPCID support

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Message-ID: <60a8347a-744d-47d3-e53b-3218f5c50623@redhat.com>
Date:   Tue, 1 Aug 2017 13:18:41 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: nVMX: INVPCID support


>> 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
> INVPCID.

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).

But you are the maintainer, so feel free to stick to what you have. :)

> 
> Paolo
> 


-- 

Thanks,

David