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

["gaoliming" <gaoliming@byosoft.com.cn>]

Tom:

> -----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. 

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
> >>
> >>
> >>
> >