Re: [PATCH for-4.22] xen/pdx: fix off-by-one index in offset mask calculation

["Roger Pau Monné" <roger.pau@citrix.com>]

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@citrix.com>
> 
> Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
> 
> > 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.