[PATCH v2] x86/shutdown: change default reboot method preference

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

The current logic to chose the preferred reboot method is based on the mode Xen
has been booted into, so if the box is booted from UEFI, the preferred reboot
method will be to use the ResetSystem() run time service call.

However, that method seems to be widely untested, and quite often leads to a
result similar to:

Hardware Dom0 shutdown: rebooting machine
----[ Xen-4.18-unstable  x86_64  debug=y  Tainted:   C    ]----
CPU:    0
RIP:    e008:[<0000000000000017>] 0000000000000017
RFLAGS: 0000000000010202   CONTEXT: hypervisor
[...]
Xen call trace:
   [<0000000000000017>] R 0000000000000017
   [<ffff83207eff7b50>] S ffff83207eff7b50
   [<ffff82d0403525aa>] F machine_restart+0x1da/0x261
   [<ffff82d04035263c>] F apic_wait_icr_idle+0/0x37
   [<ffff82d040233689>] F smp_call_function_interrupt+0xc7/0xcb
   [<ffff82d040352f05>] F call_function_interrupt+0x20/0x34
   [<ffff82d04033b0d5>] F do_IRQ+0x150/0x6f3
   [<ffff82d0402018c2>] F common_interrupt+0x132/0x140
   [<ffff82d040283d33>] F 
arch/x86/acpi/cpu_idle.c#acpi_idle_do_entry+0x113/0x129
   [<ffff82d04028436c>] F 
arch/x86/acpi/cpu_idle.c#acpi_processor_idle+0x3eb/0x5f7
   [<ffff82d04032a549>] F arch/x86/domain.c#idle_loop+0xec/0xee

****************************************
Panic on CPU 0:
FATAL TRAP: vector = 6 (invalid opcode)
****************************************

Which in most cases does lead to a reboot, however that's unreliable.

Change the default reboot preference to prefer ACPI over UEFI if available and
not in reduced hardware mode.

This is in line to what Linux does, so it's unlikely to cause issues on current
and future hardware, since there's a much higher chance of vendors testing
hardware with Linux rather than Xen.

Add a special case for one Acer model that does require being rebooted using
ResetSystem().  See Linux commit 0082517fa4bce for rationale.

I'm not aware of using ACPI reboot causing issues on boxes that do have
properly implemented ResetSystem() methods.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Changes since v1:
 - Add special case for Acer model to use UEFI reboot.
 - Adjust commit message.
---
 xen/arch/x86/shutdown.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/shutdown.c b/xen/arch/x86/shutdown.c
index 7619544d14da..3816ede1afe5 100644
--- a/xen/arch/x86/shutdown.c
+++ b/xen/arch/x86/shutdown.c
@@ -150,19 +150,20 @@ static void default_reboot_type(void)
 
     if ( xen_guest )
         reboot_type = BOOT_XEN;
+    else if ( !acpi_disabled && !acpi_gbl_reduced_hardware )
+        reboot_type = BOOT_ACPI;
     else if ( efi_enabled(EFI_RS) )
         reboot_type = BOOT_EFI;
-    else if ( acpi_disabled )
-        reboot_type = BOOT_KBD;
     else
-        reboot_type = BOOT_ACPI;
+        reboot_type = BOOT_KBD;
 }
 
 static int __init cf_check override_reboot(const struct dmi_system_id *d)
 {
     enum reboot_type type = (long)d->driver_data;
 
-    if ( type == BOOT_ACPI && acpi_disabled )
+    if ( (type == BOOT_ACPI && acpi_disabled) ||
+         (type == BOOT_EFI && !efi_enabled(EFI_RS)) )
         type = BOOT_KBD;
 
     if ( reboot_type != type )
@@ -172,6 +173,7 @@ static int __init cf_check override_reboot(const struct 
dmi_system_id *d)
             [BOOT_KBD]  = "keyboard controller",
             [BOOT_ACPI] = "ACPI",
             [BOOT_CF9]  = "PCI",
+            [BOOT_EFI]  = "UEFI",
         };
 
         reboot_type = type;
@@ -530,6 +532,15 @@ static const struct dmi_system_id __initconstrel 
reboot_dmi_table[] = {
             DMI_MATCH(DMI_PRODUCT_NAME, "PowerEdge R740"),
         },
     },
+    {    /* Handle problems with rebooting on Acer TravelMate X514-51T. */
+        .callback = override_reboot,
+        .driver_data = (void *)(long)BOOT_EFI,
+        .ident = "Acer TravelMate X514-51T",
+        .matches = {
+            DMI_MATCH(DMI_SYS_VENDOR, "Acer"),
+            DMI_MATCH(DMI_PRODUCT_NAME, "TravelMate X514-51T"),
+        },
+    },
     { }
 };
 
-- 
2.42.0