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

[Julien Grall <julien@xxxxxxx>]

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.

Cheers,

--
Julien Grall