Re: [PATCH 2/2] KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN

[Vitaly Kuznetsov]

Igor Mammedov <imammedo@xxxxxxxxxx> writes:

> On Fri, 14 Jan 2022 10:31:50 +0100
> Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> wrote:
>
>> Igor Mammedov <imammedo@xxxxxxxxxx> writes:
>> 
>> 
>> > However, a problem of failing KVM_SET_CPUID2 during VCPU re-plug
>> > is still there and re-plug will fail if KVM rejects repeated KVM_SET_CPUID2
>> > even if ioctl called with exactly the same CPUID leafs as the 1st call.
>> >  
>> 
>> Assuming APIC id change doesn not need to be supported, I can send v2
>> here with an empty allowlist.
> As you mentioned in another thread black list would be better
> to address Sean's concerns or just revert problematic commit.
>

Personally, I'm leaning towards the blocklist approach even if just for
'documenting' the fact that KVM doesn't correctly handle the
change. Compared to a comment in the code, such approach could help
someone save tons of debugging time (if anyone ever decides do something
weird, like changing MAXPHYADDR on the fly).

-- 
Vitaly