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Subject: Re: [PATCH v4] KVM: X86: Allow userspace to define the microcode
 version
To:     Wanpeng Li <kernellwp@gmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>, kvm <kvm@vger.kernel.org>,
        =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Liran Alon <liran.alon@oracle.com>,
        Nadav Amit <nadav.amit@gmail.com>
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 <CANRm+CzvN5ypz=Y2moJQph36O5tpDbqzJtB2N_8Hm3guqWXYSg@mail.gmail.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <c44a08d1-a532-879f-79dd-81c8ea175365@redhat.com>
Date:   Tue, 27 Feb 2018 11:22:32 +0100
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On 27/02/2018 10:26, Wanpeng Li wrote:
> 2018-02-27 16:38 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
>> On 27/02/2018 03:35, Wanpeng Li wrote:
>>> From: Wanpeng Li <wanpengli@tencent.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@amazon.de>
>>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>>> Cc: Radim Krčmář <rkrcmar@redhat.com>
>>> Cc: Liran Alon <liran.alon@oracle.com>
>>> Cc: Nadav Amit <nadav.amit@gmail.com>
>>> Signed-off-by: Wanpeng Li <wanpengli@tencent.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