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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 14/09/2023 4:21 pm, Roger Pau Monne wrote:
> 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 call seems to be widely untested once the firmware has exited
> boot services, and quite often leads to a result similar to:

I don't know how true this is.  What Xen does differently to most of the
rest of the world is not calling SetVirtualAddressMap()

>
> 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.
>
> 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>

Wording aside, Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

This is a giant embarrassment to Xen, and needs fixing.

> ---
> I haven't found anything in the UEFI spec that mandates to use ResetSystem()
> when booted from UEFI, I've only found:
>
> "One method of resetting the platform is through the EFI Runtime Service
> ResetSystem()."
>
> But that's vaguely a recommendation.
>
> I've found a lot of boxes that don't reboot properly using ResetSystem(), and 
> I
> think our default should attempt to make sure Xen reliably reboots on as much
> hardware as possible.

You're supposed to use ResetSystem() so all the value-add can be added
behind your back, but it's a chocolate teapot when it's so broken that
none of the OSes use it...

~Andrew