linux-kernel - Re: [PATCH v1 3/4] KVM: MMU: Add 5 level EPT & Shadow page table support.

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Date:   Mon, 14 Aug 2017 22:55:57 +0800
From:   Yu Zhang <yu.c.zhang@...ux.intel.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, rkrcmar@...hat.com,
        tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        xiaoguangrong@...cent.com, joro@...tes.org
Subject: Re: [PATCH v1 3/4] KVM: MMU: Add 5 level EPT & Shadow page table
 support.



On 8/14/2017 11:02 PM, Paolo Bonzini wrote:
> On 14/08/2017 16:32, Yu Zhang wrote:
>>
>> On 8/14/2017 10:13 PM, Paolo Bonzini wrote:
>>> On 14/08/2017 13:37, Yu Zhang wrote:
>>>> Thanks a lot for your comments, Paolo. :-)
>>>>
>>>>
>>>> On 8/14/2017 3:31 PM, Paolo Bonzini wrote:
>>>>> On 12/08/2017 15:35, Yu Zhang wrote:
>>>>>>     struct rsvd_bits_validate {
>>>>>> -    u64 rsvd_bits_mask[2][4];
>>>>>> +    u64 rsvd_bits_mask[2][5];
>>>>>>         u64 bad_mt_xwr;
>>>>>>     };
>>>>> Can you change this 4 to PT64_ROOT_MAX_LEVEL in patch 2?
>>>> Well, I had tried, but failed to find a neat approach to do so. The
>>>> difficulty I have met is that PT64_ROOT_MAX_LEVEL is defined together
>>>> with PT64_ROOT_4LEVEL/PT32E_ROOT_LEVEL/PT32_ROOT_LEVEL in mmu.h, yet
>>>> the rsvd_bits_validate structure is defined in kvm_host.h, which are
>>>> included in quite a lot .c files that do not include mmu.h or include
>>>> the mmu.h after kvm_host.h.
>>>>
>>>> I guess that's the reason why the magic number 4 instead of
>>>> PT64_ROOT_4LEVEL is used in current definition of
>>>> rsvd_bits_vadlidate. :-)
>>> Yes, you're right.  I think the solution is to define
>>> PT64_ROOT_MAX_LEVEL in kvm_host.h.
>> Thanks, Paolo. How about we also move the definition of PT64_ROOT_4LEVEL/
>> PT32E_ROOT_LEVEL/PT32_ROOT_LEVEL from mmu.h to kvm_host.h? Then we
>> can define PT64_ROOT_MAX_LEVEL as PT64_ROOT_4LEVEL instead of 4 in
>> kvm_host.h.
> No, I think those are best left in mmu.h.  They are only used in mmu
> files, except for two occurrences in svm.c.
>
> kvm_host.h would have PT64_ROOT_MAX_LEVEL just because it is slightly
> better than "4" or "5".

OK. I can define PT64_ROOT_MAX_LEVEL in kvm_host.h as 4 in patch 2, and 
change
it to 5 in patch 3. :- )

Thanks
Yu