On Fri, 1 Nov 2024 at 18:49, Lorenzo Pieralisi <lpieralisi@xxxxxxxxxx> wrote:
>
> [+Ard, Sami, for EFI]
>
> On Thu, Oct 31, 2024 at 06:55:43PM +0100, Lorenzo Pieralisi wrote:
> > On Sat, Oct 19, 2024 at 06:15:47PM +0100, David Woodhouse wrote:
> >
> > [...]
> >
> > > +#ifdef CONFIG_HIBERNATION
> > > +static int psci_sys_hibernate(struct sys_off_data *data)
> > > +{
> > > + /*
> > > + * Zero is an acceptable alternative to PSCI_1_3_OFF_TYPE_HIBERNATE_OFF
> > > + * and is supported by hypervisors implementing an earlier version
> > > + * of the pSCI v1.3 spec.
> > > + */
> >
> > It is obvious but with this patch applied a host kernel would start executing
> > SYSTEM_OFF2 too if supported in firmware to hibernate, it is not a hypervisor
> > only code path.
> >
> > Related to that: is it now always safe to override
> >
> > commit 60c0d45a7f7a ("efi/arm64: use UEFI for system reset and poweroff")
> >
> > for hibernation ? It is not very clear to me why overriding PSCI for
> > poweroff was the right thing to do - tried to follow that patch history but
> > the question remains (it is related to UpdateCapsule() but I don't know
> > how that applies to the hibernation use case).
>
> RFC: It is unclear to me what happens in current mainline if we try to
> hibernate with EFI runtime services enabled and a capsule update pending (we
> issue EFI ResetSystem(EFI_RESET_SHUTDOWN,..) which might not be compatible
> with the reset required by the pending capsule update request) what happens
> in this case I don't know but at least the choice is all contained in
> EFI firmware.
>
> Then if in the same scenario now we are switching to PSCI SYSTEM_OFF2 for the
> hibernate reset I suspect that what happens to the in-flight capsule
> update requests strictly depends on what "reset" PSCI SYSTEM_OFF2 will
> end up doing ?
>
> I think this is just a corner case and it is unlikely it has been ever
> tested (is it even possible ? Looking at EFI folks) - it would be good
> to clarify it at least to make sure we understand this code path.
>
I'm not aware of any OS that actually uses capsule update at runtime
(both Windows and Linux queue up the capsule and call the
UpdateCapsule() runtime service at boot time after a reboot).
So it is unlikely that this would break anything, and I'd actually be
inclined to disable capsule update at runtime altogether.
I will also note that hibernation with EFI is flaky in general, given
that EFI memory regions may move around
