Re: 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 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.

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
>>
>>
>>
>