linux-kernel - Re: [PATCH v3 01/10] KVM: MMU: fix decoding cache type from MTRR

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Message-ID: <55A3D616.8010209@linux.intel.com>
Date:	Mon, 13 Jul 2015 23:15:34 +0800
From:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
To:	Paolo Bonzini <pbonzini@...hat.com>,
	Alex Williamson <alex.williamson@...hat.com>
CC:	gleb@...nel.org, mtosatti@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 01/10] KVM: MMU: fix decoding cache type from MTRR



On 07/13/2015 11:13 PM, Paolo Bonzini wrote:
> On 13/07/2015 16:45, Xiao Guangrong wrote:
>>> +    /* MTRR is completely disabled, use UC for all of physical
>>> memory. */
>>> +    if (!(mtrr_state->enabled & 0x2))
>>> +        return MTRR_TYPE_UNCACHABLE;
>>>
>>> actually disappears in commit fa61213746a7 (KVM: MTRR: simplify
>>> kvm_mtrr_get_guest_memory_type, 2015-06-15).
>>
>> :(
>>
>> Based on the SDM, UC is applied to all memory rather than default-type
>> if MTRR is disabled.
>
> There are two issues I think.  One is that I cannot find in the current
> code that "UC is applied to all memory rather than default-type if MTRR
> is disabled".  mtrr_default_type unconditionally looks at
> mtrr_state->deftype.

Yes... Will fix.

>
>> However, fast boot came back if "return 0xFF" here. So fast boot expects
>> that the memory type is WB.
>
> Yes.
>
>>>
>>> static u8 mtrr_default_type(struct kvm_mtrr *mtrr_state)
>>> {
>>>           if (mtrr_is_enabled(mtrr_state))
>>>                   return mtrr_state->deftype &
>>> IA32_MTRR_DEF_TYPE_TYPE_MASK;
>>>           else
>>>                   return MTRR_TYPE_UNCACHABLE;
>>> }
>>>
>>> ?  Then it's easy to add a quirk that makes the default WRITEBACK until
>>> MTRRs are enabled.
>>
>> It is the wrong configure in OVMF... shall we need to adjust KVM to satisfy
>> OVMF?
>
> That's what quirks are for...  The firmware should still be fixed of course.

I see, will do it.
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