linux-kernel - Re: [PATCH] kvm: VMX: do not use vm-exit instruction length for fast MMIO

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Message-ID: <3f6fd875-037c-91c8-b570-d5010751d175@redhat.com>
Date:   Fri, 18 Aug 2017 14:41:52 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     rkrcmar@...hat.com, "Michael S. Tsirkin" <mst@...hat.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] kvm: VMX: do not use vm-exit instruction length for fast
 MMIO

On 18.08.2017 14:35, Paolo Bonzini wrote:
> On 18/08/2017 13:57, David Hildenbrand wrote:
>> What about a hack:
>>
>> 1. clear instruction length when entering
>> 2. check if instruction length is set when trying to forward the RIP
>> 2a. if set, use it
>> 2b. if not set, compute it
> 
> It's undefined, so we don't know that the instruction length remains
> zero (also, on older processors and possibly some nested setups the
> field is read-only).

Oh I see, too bad :(

> 
> Testing the hypervisor bit is the first line of action.
> 
> Paolo


-- 

Thanks,

David