[PATCH] x86/acpi: fix suspend with Xen

[Juergen Gross <jgross@xxxxxxxx>]

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).

Fixes: f1e525009493 ("x86/boot: Skip realmode init code when running as Xen PV 
guest")
Reported-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 arch/x86/include/asm/acpi.h  | 2 +-
 arch/x86/kernel/acpi/sleep.c | 3 ++-
 include/xen/acpi.h           | 9 +++++++++
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/acpi.h b/arch/x86/include/asm/acpi.h
index 65064d9f7fa6..137259ff8f03 100644
--- a/arch/x86/include/asm/acpi.h
+++ b/arch/x86/include/asm/acpi.h
@@ -61,7 +61,7 @@ static inline void acpi_disable_pci(void)
 extern int (*acpi_suspend_lowlevel)(void);
 
 /* Physical address to resume after wakeup */
-unsigned long acpi_get_wakeup_address(void);
+extern unsigned long (*acpi_get_wakeup_address)(void);
 
 /*
  * Check if the CPU can handle C2 and deeper
diff --git a/arch/x86/kernel/acpi/sleep.c b/arch/x86/kernel/acpi/sleep.c
index 3b7f4cdbf2e0..1a3cd5e24cd0 100644
--- a/arch/x86/kernel/acpi/sleep.c
+++ b/arch/x86/kernel/acpi/sleep.c
@@ -33,10 +33,11 @@ static char temp_stack[4096];
  * Returns the physical address where the kernel should be resumed after the
  * system awakes from S3, e.g. for programming into the firmware waking vector.
  */
-unsigned long acpi_get_wakeup_address(void)
+static unsigned long x86_acpi_get_wakeup_address(void)
 {
        return ((unsigned long)(real_mode_header->wakeup_start));
 }
+unsigned long (*acpi_get_wakeup_address)(void) = x86_acpi_get_wakeup_address;
 
 /**
  * x86_acpi_enter_sleep_state - enter sleep state
diff --git a/include/xen/acpi.h b/include/xen/acpi.h
index b1e11863144d..7e1e5dbfb77c 100644
--- a/include/xen/acpi.h
+++ b/include/xen/acpi.h
@@ -56,6 +56,12 @@ static inline int xen_acpi_suspend_lowlevel(void)
        return 0;
 }
 
+static inline unsigned long xen_acpi_get_wakeup_address(void)
+{
+       /* Just return a dummy non-zero value, it will never be used. */
+       return 1;
+}
+
 static inline void xen_acpi_sleep_register(void)
 {
        if (xen_initial_domain()) {
@@ -65,6 +71,9 @@ static inline void xen_acpi_sleep_register(void)
                        &xen_acpi_notify_hypervisor_extended_sleep);
 
                acpi_suspend_lowlevel = xen_acpi_suspend_lowlevel;
+#ifdef CONFIG_ACPI_SLEEP
+               acpi_get_wakeup_address = xen_acpi_get_wakeup_address;
+#endif
        }
 }
 #else
-- 
2.35.3