linux-kernel - Re: KVM_SET_CPUID doesn't check supported bits (was Re: [PATCH 0/6] KVM: x86: KVM_SET

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Message-ID: <ae433269-61ee-9bb8-0e06-a266b10c7f31@yandex.ru>
Date:   Mon, 7 Dec 2020 17:41:26 +0300
From:   stsp <stsp2@...dex.ru>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: KVM_SET_CPUID doesn't check supported bits (was Re: [PATCH 0/6]
 KVM: x86: KVM_SET_SREGS.CR4 bug fixes and cleanup)

07.12.2020 17:34, Paolo Bonzini пишет:
>
>     > It is too late to change that aspect of the API, unfortunately. We
>     > don't know how various userspaces would behave.
>     Which means some sensible behaviour
>     already exists if I don't call KVM_SET_CPUID2.
>     So what is it, #UD on CPUID?
>
>
> I would have to check but I think you always get zeroes; not entirely 
> sensible.
In that case I would argue that you can't
break anything by changing that to something
sensible. :)
But anyway, since my problem is solved,
this is just a potential improvement for the
future, or the case for documenting.