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Re: [PATCH 3/3] gnttab: GTF_sub_page is a v2-only flag
- To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 18 Feb 2021 14:22:49 +0000
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- Cc: George Dunlap <george.dunlap@xxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 17/02/2021 10:46, Jan Beulich wrote:
> Prior to its introduction, v1 entries weren't checked for this flag, and
> the flag also has been meaningless for v1 entries. Therefore it also
> shouldn't be checked. (The only consistent alternative would be to also
> check for all currently undefined flags to be clear.)
We recently had a similar discussion for the stable libs.
Whatever we do, an unexpected corner case needs to break. Checking for
all undefined flags up front is far cleaner - absolutely nothing good
can come for a guest which set GTF_sub_page with v1, and is expecting it
to work, and this way, we do all breaking in one go, rather than
breaking $N times in the future as new flags get added.
~Andrew
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