Re: 回复: 回复: 回复: [PATCH v2 01/11] MdePkg, OvmfPkg: Clean up GHCB field offsets and save area

["Lendacky, Thomas" <thomas.lendacky@amd.com>]

On 10/20/20 7:54 PM, gaoliming wrote:
> Tom:

Hi Liming,

> 
>> -----邮件原件-----
>> 发件人: Tom Lendacky <thomas.lendacky@amd.com>
>> 发送时间: 2020年10月20日 21:10
>> 收件人: Laszlo Ersek <lersek@redhat.com>; gaoliming
>> <gaoliming@byosoft.com.cn>; devel@edk2.groups.io
>> 抄送: 'Brijesh Singh' <brijesh.singh@amd.com>; 'Michael D Kinney'
>> <michael.d.kinney@intel.com>; 'Zhiguang Liu' <zhiguang.liu@intel.com>;
>> 'Jordan Justen' <jordan.l.justen@intel.com>; 'Ard Biesheuvel'
>> <ard.biesheuvel@arm.com>
>> 主题: Re: 回复: 回复: [PATCH v2 01/11] MdePkg, OvmfPkg: Clean up GHCB
>> field offsets and save area
>>
>> On 10/20/20 3:31 AM, Laszlo Ersek wrote:
>>> On 10/20/20 03:08, gaoliming wrote:
>>>> Laszlo and Tom:
>>>>
>>>>> -----邮件原件-----
>>>>> 发件人: Laszlo Ersek <lersek@redhat.com>
>>>>> 发送时间: 2020年10月20日 4:42
>>>>> 收件人: Tom Lendacky <thomas.lendacky@amd.com>; gaoliming
>>>>> <gaoliming@byosoft.com.cn>; devel@edk2.groups.io
>>>>> 抄送: 'Brijesh Singh' <brijesh.singh@amd.com>; 'Michael D Kinney'
>>>>> <michael.d.kinney@intel.com>; 'Zhiguang Liu' <zhiguang.liu@intel.com>;
>>>>> 'Jordan Justen' <jordan.l.justen@intel.com>; 'Ard Biesheuvel'
>>>>> <ard.biesheuvel@arm.com>
>>>>> 主题: Re: 回复: [PATCH v2 01/11] MdePkg, OvmfPkg: Clean up GHCB
>> field
>>>>> offsets and save area
>>>>>
>>>>> On 10/19/20 14:50, Tom Lendacky wrote:
>>>>>> On 10/18/20 8:41 PM, gaoliming wrote:
>>>>>
>>>>>>> Please separate the patch for the change in OvmfPkg.
>>>>>>> One commit can't cross the different packages.
>>>>>>> I understand this is the incompatible change. But, we still need to
>> follow
>>>>>>> this rule.
>>>>>
>>>>> I disagree.
>>>>>
>>>>> We should do whatever we can for avoiding cross-package patches, but in
>>>>> some cases, they are unavoidable. This is one of those cases.
>>>>
>>>> I suggest to define enum GHCB_QWORD_OFFSET, then use typedef
>> GHCB_QWORD_OFFSET GHCB_REGISTER; in Ghcb.h
>>>> The comments can be added here to describe it is for compatibility. The old
>> one is not recommend.
>>>>
>>>> Then, the change in MdePkg is compatible. Next patch is to update
>> OvmfPkg VmgExit to consume GHCB_QWORD_OFFSET.
>>>
>>> Ah, I totally missed that we could use typedef to bridge the gap. That
>>> indeed allows us to do the rename in three steps (only for the type
>>> name, the enum constant identifiers can stay the same). After the
>>> rename, the enum constant values can be cleaned up in a separate (4th)
>>> patch.
>>
>> It seems like a lot of churn for just renaming. If there are no
>> objections, I'll keep the GHCB_REGISTER name. The important piece is the
>> change from hardcoding the offset values to using a calculated value.
>>
> I am fine to keep current GHCB_REGISTER name. 

This raises a question about patch 10 of the series. Since that patch
changes interfaces, I included both the UefiCpuPkg and OvmfPkg changes in
that one patch. Will that be acceptable?

Thanks,
Tom

> 
> Thanks
> Liming
> 
>> Thanks,
>> Tom
>>
>>>
>>> Thank you!
>>> Laszlo
>>>
>>>>
>>>> Thanks
>>>> Liming
>>>>>
>>>>>> Ok, then I'll resubmit without the name change. To me, it's not worth
>>>>>> doing 3 commits just to accomplish the rename from GHCB_REGISTER to
>>>>>> GHCB_QWORD_OFFSET.
>>>>>
>>>>> When reviewing v1, I immediately thought of doing the rename in 3
>>>>> commits (introduce new type, rebase client sites, remove old type). I
>>>>> didn't suggest it because it wouldn't work.
>>>>>
>>>>> I wrote:
>>>>>
>>>>>     we are not changing the identifiers of the enumeration constants
>>>>>     (such as GhcbCpl). Because those identifiers are declared at file
>>>>>     scope, having both GHCB_REGISTER and GHCB_QWORD_OFFSET
>>>>> declare
>>>>>     (e.g.) GhcbCpl would cause a compilation failure. Therefore we can't
>>>>>     implement this in multiple stages (first introduce
>>>>>     GHCB_QWORD_OFFSET, then remove GHCB_REGISTER separately).
>>>>>
>>>>> In other words, if we attempted to do this in 3 stages, then the 2nd
>>>>> patch (introducing the new type, in addition to the old type) would not
>>>>> compile. The new type could not reuse the old type's enum constants
>>>>> (their identifiers). So we'd either have to change the enum constant
>>>>> names of the old type (and then we'd be back to square 1 -- the client
>>>>> sites would have to be migrated in the same patch), or introduce the new
>>>>> type with new enum constant names as well. But then, the client sites
>>>>> would have to be migrated to the new enum constant names as well, not
>>>>> just the new enum type name.
>>>>>
>>>>> This is why I said that, IMO, in this case a cross-package patch was
>>>>> acceptable. Because otherwise we could never rename an enum type
>> without
>>>>> also renaming the enum constants.
>>>>>
>>>>> Thanks
>>>>> Laszlo
>>>>
>>>>
>>>>
>>>
> 
>