Re: [PATCH] x86/acpi: fix suspend with Xen

["Rafael J. Wysocki" <rafael@xxxxxxxxxx>]

On Tue, Jan 17, 2023 at 4:32 PM Juergen Gross <jgross@xxxxxxxx> wrote:
>
> On 17.01.23 15:09, Rafael J. Wysocki wrote:
> > On Mon, Jan 16, 2023 at 7:45 AM Juergen Gross <jgross@xxxxxxxx> wrote:
> >>
> >> On 13.01.23 20:40, Rafael J. Wysocki wrote:
> >>> On Fri, Jan 13, 2023 at 3:06 PM Juergen Gross <jgross@xxxxxxxx> wrote:
> >>>>
> >>>> Commit f1e525009493 ("x86/boot: Skip realmode init code when running as
> >>>> Xen PV guest") missed one code path accessing real_mode_header, leading
> >>>> to dereferencing NULL when suspending the system under Xen:
> >>>>
> >>>>       [  348.284004] PM: suspend entry (deep)
> >>>>       [  348.289532] Filesystems sync: 0.005 seconds
> >>>>       [  348.291545] Freezing user space processes ... (elapsed 0.000 
> >>>> seconds) done.
> >>>>       [  348.292457] OOM killer disabled.
> >>>>       [  348.292462] Freezing remaining freezable tasks ... (elapsed 
> >>>> 0.104 seconds) done.
> >>>>       [  348.396612] printk: Suspending console(s) (use 
> >>>> no_console_suspend to debug)
> >>>>       [  348.749228] PM: suspend devices took 0.352 seconds
> >>>>       [  348.769713] ACPI: EC: interrupt blocked
> >>>>       [  348.816077] BUG: kernel NULL pointer dereference, address: 
> >>>> 000000000000001c
> >>>>       [  348.816080] #PF: supervisor read access in kernel mode
> >>>>       [  348.816081] #PF: error_code(0x0000) - not-present page
> >>>>       [  348.816083] PGD 0 P4D 0
> >>>>       [  348.816086] Oops: 0000 [#1] PREEMPT SMP NOPTI
> >>>>       [  348.816089] CPU: 0 PID: 6764 Comm: systemd-sleep Not tainted 
> >>>> 6.1.3-1.fc32.qubes.x86_64 #1
> >>>>       [  348.816092] Hardware name: Star Labs StarBook/StarBook, BIOS 
> >>>> 8.01 07/03/2022
> >>>>       [  348.816093] RIP: e030:acpi_get_wakeup_address+0xc/0x20
> >>>>
> >>>> Fix that by adding an indirection for acpi_get_wakeup_address() which
> >>>> Xen PV dom0 can use to return a dummy non-zero wakeup address (this
> >>>> address won't ever be used, as the real suspend handling is done by the
> >>>> hypervisor).
> >>>
> >>> How exactly does this help?
> >>
> >> I believed the first sentence of the commit message would make this
> >> clear enough.
> >
> > That was clear, but the fix part wasn't really.
> >
> >> I can expand the commit message to go more into detail if you think
> >> this is really needed.
> >
> > IMO calling acpi_set_waking_vector() with a known-invalid wakeup
> > vector address in dom0 is plain confusing.
> >
> > I'm not sure what to do about it yet, but IMV something needs to be done.
>
> Another possibility would be to modify acpi_sleep_prepare(), e.g. like the
> attached patch (compile tested only).

I prefer this to the previous version.  It is much more straightforward IMV.