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Re: [PATCH for-4.22] xen/pdx: fix off-by-one index in offset mask calculation
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Tue, 9 Jun 2026 11:14:52 +0200
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- Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>
- Delivery-date: Tue, 09 Jun 2026 09:15:15 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Tue, Jun 09, 2026 at 09:59:37AM +0100, Andrew Cooper wrote:
> On 09/06/2026 9:53 am, Roger Pau Monne wrote:
> > Adjust the mask calculation in case the last range is merged with the
> > previous one, as then the mask must be calculated from the previous range,
> > which the current one has been merged into.
> >
> > Instead of fixing the off-by-one in place, move the calculation of the bit
> > change mask to the next loop, after the ranges have been merged. This
> > simplifies the logic by consolidating mask calculation in a single place,
> > possibly making it less error prone in the future.
> >
> > Also add a test case that triggers the bug being fixed by this commit.
> >
> > Fixes: c5c45bcbd6a1 ("pdx: introduce a new compression algorithm based on
> > region offsets")
> > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>
> Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>
> > diff --git a/tools/tests/pdx/test-pdx.c b/tools/tests/pdx/test-pdx.c
> > index d783186577ef..ba57f1793011 100644
> > --- a/tools/tests/pdx/test-pdx.c
> > +++ b/tools/tests/pdx/test-pdx.c
> > @@ -191,6 +191,20 @@ int main(int argc, char **argv)
> > },
> > .compress = false,
> > },
> > + /*
> > + * 2s Dell R740, merging of ranges causes mask differences in PDX
> > + * offset mode. Useful for checking mask calculations.
>
> What's the 2s here? If it is what I think it is, I'd suggest "Dell
> R740, dual socket,"
Yes, it's what you think it is. I've used "2s" in existing comments,
but I'm perfectly fine with spelling it out.
Thanks, Roger.
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