Re: [PATCH for-4.22?] xen/arm: mask debug exceptions in initial AArch64 guest state

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

Hello Mykola and Julien,

On 6/21/26 4:30 PM, Mykola Kvach wrote:
> Hi Julien,
>
> Thanks for the review.
>
> On Sat, Jun 20, 2026 at 12:07 AM Julien Grall <julien@xxxxxxx> wrote:
> > Hi Mykola,
> >
> > On 19/06/2026 19:37, Mykola Kvach wrote:
> > > PSR_GUEST64_INIT currently masks SError, IRQ and FIQ, but leaves debug
> > > exceptions unmasked. Both the AArch64 Linux boot protocol and PSCI entry
> > > requirements expect PSTATE.DAIF to be masked.
> > >
> > > Add PSR_DBG_MASK to PSR_GUEST64_INIT. This fixes the initial AArch64 guest
> > > entry state as well as virtual PSCI CPU_ON and SYSTEM_SUSPEND resume entry.
> > >
> > > Signed-off-by: Mykola Kvach <mykola_kvach@xxxxxxxx>
> > Reviewed-by: Julien Grall <julien@xxxxxxx>
> >
> > Regarding Xen 4.22, I understand and agree this is technically against
> > the specification. However, AFAIR, we don't expose debug registers to
> > the guest. So there should be no impact.
> >
> > The slight risk with this patch is OS that may have started to rely on
> > Xen behavior (hopefully not here, but I know we had a couple of cases
> > with the timer for instance...).
> >
> > This has been present forever. So unless there is a real issue, I am
> > tempted to suggest to wait until the release is out and backport after.
> >
> > I will leave Oleksii the final decision.
> I agree with your assessment. I am fine with deferring this until after the
> release unless Oleksii decides otherwise.
>
> The patch is not fixing any known issue and was only intended to align the
> guest entry state with the documented requirements.
If it isn't fixing any known issue then lets defer this patch until 4.22 
will be released.
Thanks.

~ Oleksii