acpi: Fix suspend with Xen PV

Commit f1e5250 ("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 optional acpi callback allowing to skip setting
the wakeup address, as in the Xen PV case this will be handled by the
hypervisor anyway.

Fixes: f1e5250 ("x86/boot: Skip realmode init code when running as Xen PV guest")
Reported-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/all/20230117155724.22940-1-jgross%40suse.com

arch/x86/include/asm/acpi.h

@@ -14,6 +14,7 @@
 #include <asm/mmu.h>
 #include <asm/mpspec.h>
 #include <asm/x86_init.h>
+#include <asm/cpufeature.h>
 
 #ifdef CONFIG_ACPI_APEI
 # include <asm/pgtable_types.h>
@@ -63,6 +64,13 @@ extern int (*acpi_suspend_lowlevel)(void);
 /* Physical address to resume after wakeup */
 unsigned long acpi_get_wakeup_address(void);
 
+static inline bool acpi_skip_set_wakeup_address(void)
+{
+	return cpu_feature_enabled(X86_FEATURE_XENPV);
+}
+
+#define acpi_skip_set_wakeup_address acpi_skip_set_wakeup_address
+
 /*
  * Check if the CPU can handle C2 and deeper
  */

drivers/acpi/sleep.c

@@ -60,13 +60,17 @@ static struct notifier_block tts_notifier = {
 	.priority	= 0,
 };
 
+#ifndef acpi_skip_set_wakeup_address
+#define acpi_skip_set_wakeup_address() false
+#endif
+
 static int acpi_sleep_prepare(u32 acpi_state)
 {
 #ifdef CONFIG_ACPI_SLEEP
 	unsigned long acpi_wakeup_address;
 
 	/* do we have a wakeup address for S2 and S3? */
-	if (acpi_state == ACPI_STATE_S3) {
+	if (acpi_state == ACPI_STATE_S3 && !acpi_skip_set_wakeup_address()) {
 		acpi_wakeup_address = acpi_get_wakeup_address();
 		if (!acpi_wakeup_address)
 			return -EFAULT;