linux-kernel - Re: [PATCH] KVM: nVMX: Filter out all unsupported controls when eVMCS was activated

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Message-ID: <6e97f33c-e4d4-5669-c642-a904c9e22a8d@redhat.com>
Date:   Wed, 22 Sep 2021 16:07:13 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     kvm@...r.kernel.org, Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: nVMX: Filter out all unsupported controls when eVMCS
 was activated

On 09/09/21 09:03, Vitaly Kuznetsov wrote:
> Sean Christopherson <seanjc@...gle.com> writes:
> 
>> On Tue, Sep 07, 2021, Vitaly Kuznetsov wrote:
>>> Let's be bold this time and instead of playing whack-a-mole just filter out
>>> all unsupported controls from VMX MSRs.
>>
>> Out of curiosity, why didn't we do this from the get-go?
> 
> We actually did, the initial implementation (57b119da3594f) was
> filtering out everything but then things changed in "only clear controls
> which are known to cause issues" (31de3d2500e4). I forgot everything
> already but was able to google this suggestion from Paolo:
> 
> https://www.lkml.org/lkml/2020/1/22/1108

The doubt was whether userspaces could be enabling eVMCS blindly, and 
thus would lose features for Linux guests.

Paolo