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

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Date:   Mon, 16 Jan 2023 07:45:26 +0100
From:   Juergen Gross <jgross@...e.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-pm@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Len Brown <len.brown@...el.com>,
        Pavel Machek <pavel@....cz>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        xen-devel@...ts.xenproject.org,
        Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>
Subject: Re: [PATCH] x86/acpi: fix suspend with Xen

On 13.01.23 20:40, Rafael J. Wysocki wrote:
> On Fri, Jan 13, 2023 at 3:06 PM Juergen Gross <jgross@...e.com> 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.

I can expand the commit message to go more into detail if you think
this is really needed.


Juergen

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