Re: [PATCH v8 10/13] xen/arm: Resume memory management on Xen resume

[Mykola Kvach <xakep.amatop@xxxxxxxxx>]

On Fri, May 8, 2026 at 4:28 PM Luca Fancellu <Luca.Fancellu@xxxxxxx> wrote:
>
> Hi Mykola,
>
> >>> xen/arch/arm/arm64/head.S | 24 ++++++++++++++++++++++++
> >>> 1 file changed, 24 insertions(+)
> >>>
> >>> diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
> >>> index 72c7b24498..596e960152 100644
> >>> --- a/xen/arch/arm/arm64/head.S
> >>> +++ b/xen/arch/arm/arm64/head.S
> >>> @@ -561,6 +561,30 @@ END(efi_xen_start)
> >>>
> >>> #endif /* CONFIG_ARM_EFI */
> >>>
> >>> +#ifdef CONFIG_SYSTEM_SUSPEND
> >>> +
> >>> +FUNC(hyp_resume)
> >>
> >> I think we should mask all exceptions here:
> >> msr DAIFSet, 0xf
> >>
> >> until we resume correctly the status (VBAR_EL2, etc).
> >
> > This was discussed in an earlier version:
> >
> > https://patchew.org/Xen/cover.1741164138.git.xakep.amatop@xxxxxxxxx/2ef15cb605f987eb087c5496d123c47c01cc0ae7.1741164138.git.xakep.amatop@xxxxxxxxx/#CAGeoDV97no7mXSKd7auFu5E85wSXAHKWvqGW2=-VEAbkrTyU8Q@xxxxxxxxxxxxxx
> >
> > For SYSTEM_SUSPEND, PSCI ties the call semantics to CPU_SUSPEND. In
> > particular, section 5.20.2 says that the caller must observe all the rules
> > described for CPU_SUSPEND, and section 6.4 explicitly says that the initial
> > state rules also apply to SYSTEM_SUSPEND.
> >
> > For the return Exception level on AArch64, section 6.4.3.3 requires
> > SPSR_ELx.{D,A,I,F} to be set to {1, 1, 1, 1}. Therefore Xen expects to enter
> > this resume path with DAIF already masked by PSCI-compliant firmware.
> >
> > I agree this assumption is not obvious from the code, so I will add a 
> > comment
> > at the resume entry point to document that this path relies on the PSCI 
> > initial
> > core configuration requirements.
>
> Yes please, something along the line of
>
> /*
>  * PSCI SYSTEM_SUSPEND follows CPU_SUSPEND initial-state rules.
>  * On AArch64, firmware must return with SPSR_ELx.DAIF set, so
>  * PSTATE.DAIF is already masked on entry here.
>  */

Ack.

Best regards,
Mykola

>
> Cheers,
> Luca
>