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Re: [PATCH] x86/pod: fix decrease_reservation() clearing of M2P entries
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Wed, 10 Dec 2025 11:10:57 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Wed, 10 Dec 2025 10:11:18 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Wed, Dec 10, 2025 at 11:07:00AM +0100, Jan Beulich wrote:
> On 10.12.2025 10:35, Roger Pau Monne wrote:
> > Add the missing index increase in the M2P clearing loop, otherwise the loop
> > keeps pointlessly setting the same MFN entry repeatedly. This seems to be
> > an oversight from the change that introduced support to process high order
> > pages in one go.
>
> Ouch.
>
> > Fixes: 3c352011c0d3 ("x86/PoD: shorten certain operations on higher order
> > ranges")
> > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> I'd like to note that things were broken in the same way before that commit,
> too, simply because the order wasn't taken into account all. (This is not a
> request to change the Fixes: tag, though. It's just an observation.)
Are you sure? Previous to that commit the order is not taken into
account, and each 4K page is processed independently: the `i` index is
strictly increased with +1 for each loop.
Thanks, Roger.
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