linux-kernel - Re: [PATCH] KVM: x86: Deflect unknown MSR accesses to user space

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Date:   Wed, 29 Jul 2020 11:09:26 +0200
From:   Alexander Graf <graf@...zon.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>
CC:     Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm list <kvm@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Aaron Lewis <aaronlewis@...gle.com>
Subject: Re: [PATCH] KVM: x86: Deflect unknown MSR accesses to user space



On 29.07.20 10:23, Vitaly Kuznetsov wrote:
> 
> 
> 
> Jim Mattson <jmattson@...gle.com> writes:
> 
>> On Tue, Jul 28, 2020 at 5:41 AM Alexander Graf <graf@...zon.com> wrote:
>>>
> 
> ...
> 
>>> While it does feel a bit overengineered, it would solve the problem that
>>> we're turning in-KVM handled MSRs into an ABI.
>>
>> It seems unlikely that userspace is going to know what to do with a
>> large number of MSRs. I suspect that a small enumerated list will
>> suffice.
> 
> The list can also be 'wildcarded', i.e.
> {
>   u32 index;
>   u32 mask;
>   ...
> }
> 
> to make it really short.

I like the idea of wildcards, but I can't quite wrap my head around how 
we would implement ignore_msrs in user space with them?


Alex



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