linux-kernel - Re: [PATCH v4] KVM: X86: Allow userspace to define the microcode version

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Date:   Tue, 27 Feb 2018 11:22:32 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Liran Alon <liran.alon@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>
Subject: Re: [PATCH v4] KVM: X86: Allow userspace to define the microcode
 version

On 27/02/2018 10:26, Wanpeng Li wrote:
> 2018-02-27 16:38 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
>> On 27/02/2018 03:35, Wanpeng Li wrote:
>>> From: Wanpeng Li <wanpengli@...cent.com>
>>>
>>> Linux (among the others) has checks to make sure that certain features
>>> aren't enabled on a certain family/model/stepping if the microcode version
>>> isn't greater than or equal to a known good version.
>>>
>>> By exposing the real microcode version, we're preventing buggy guests that
>>> don't check that they are running virtualized (i.e., they should trust the
>>> hypervisor) from disabling features that are effectively not buggy.
>>>
>>> Suggested-by: Filippo Sironi <sironi@...zon.de>
>>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>>> Cc: Liran Alon <liran.alon@...cle.com>
>>> Cc: Nadav Amit <nadav.amit@...il.com>
>>> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
>>> ---
>>> v3 -> v4:
>>>  * add the shifts back
>>
>> Please wait for a review instead of pushing new versions continuously.
>> Leaving the shifts means that MSR_IA32_UCODE_REV's bits 0-31 are zeroed
>> even if KVM_SET_MSRS makes them nonzero.
> 
> How about something like this?

Yes, that's okay.

Paolo