Re: [PATCH v2] memory: overlapping XENMAPSPACE_gmfn_range requests

[Andrew Cooper <andrew.cooper3@citrix.com>]

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@citrix.com>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> ---
> 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@citrix.com>
Tested-by: Andrew Cooper <andrew.cooper3@citrix.com>

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