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

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

On Thu, Sep 14, 2023 at 06:42:03PM +0100, Andrew Cooper wrote:
> 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()

Hm, but that doesn't seem to affect the rest of the run-time services
(at least on this box), it's (just?) ResetSystem() that misbehaves.

I can remove that sentence however, it is more of a guess rather than
a fact.

> 
> >
> > 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.

Looking at Linux I think we need to add an override for Acer
TravelMate X514-51T to force it to use UEFI, will send v2 with it.

I do wonder if we need to keep the reboot_dmi_table[] entries that
force systems to use ACPI, as it would now be the default?  My
thinking is that it's likely better to keep it just in case we change
the default again in the future.

Thanks, Roger.