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Re: [PATCH v2] memory: overlapping XENMAPSPACE_gmfn_range requests
- To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 12 May 2026 17:00:39 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Tue, 12 May 2026 16:00:52 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 22/12/2025 10:33 am, Jan Beulich wrote:
> Overlapping requests may need processing backwards, or else the intended
> effect wouldn't be achieved (and instead some pages would be moved more
> than once).
>
> With some adjustment there this also covers XEN_DMOP_relocate_memory,
> where the potential issue was first noticed.
>
> Fixes: a04811a315e0 ("mm: New XENMEM space, XENMAPSPACE_gmfn_range")
> Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> Of course an alternative would be to simply reject overlapping requests.
> Then we should reject all overlaps though, I think. But since the code
> change didn't end up overly intrusive, I thought I would go the "fix it"
> route first.
> ---
> v2: Adjust XEN_DMOP_relocate_memory handling for the working-backwards
> case.
Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Tested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
I can't say that I've understood everything going on here (hence the
test case), but the test case says it does fix the bug I reported.
~Andrew
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