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

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

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.