Re: [PATCH 2/5] llc-coloring: improve checking while parsing

[Mykola Kvach <xakep.amatop@xxxxxxxxx>]

On Wed, Mar 25, 2026 at 8:14 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>
> On 24.03.2026 17:51, Mykola Kvach wrote:
> > On Tue, Mar 24, 2026 at 6:37 PM Jan Beulich <jbeulich@xxxxxxxx> wrote:
> >>
> >> We can easily avoid the risk of wrapping UINT_MAX <-> 0 by applying a
> >> check against the compile-time-constant maximum number of colors.
> >>
> >> Additionally the overflow checks suffered from an off-by-1, as the parsed
> >> ranges are inclusive (e.g. end == start being possible, requiring 1 array
> >> slot, while availability of 0 slots was checked in that case).
> >>
> >> Fixes: 6cdea3444eaf ("xen/arm: add Dom0 cache coloring support")
> >> Reported-by: Kamil Frankowicz <kamil.frankowicz@xxxxxxx>
> >
> > For reference, I previously reported the UINT_MAX wraparound aspect here [1]
> > and later also here [2].
>
> I've added another Reported-by, yet I wonder (in particular wrt [2]): Why did
> you not simply send patches? They likely would long have gone in.

Thank you.

I did not have the time earlier to turn those reports into proper patches.

This month I have had some bandwidth again, so I started revisiting a number
of previously reported issues.

At the moment I am also preparing some other fixes related to ITS, and the
LLC issues were next on my list.


Best regards,
Mykola


>
> Jan
>
> > The off-by-1 in the inclusive-range accounting looks
> > like a separate issue.
> >
> > Those threads also mention a few other related corner cases.
> >
> >
> > Best regards,
> > Mykola
> >
> >
> > [1] 
> > https://patchew.org/Xen/20241217170637.233097-1-carlo.nonato@xxxxxxxxxxxxxxx/20241217170637.233097-5-carlo.nonato@xxxxxxxxxxxxxxx/#db5d6a67-61d9-48d3-b6c4-213c1cbbda21@xxxxxxxxx
> > [2] https://lists.xen.org/archives/html/xen-devel/2026-01/msg00369.html