On Wed, Sep 27, 2023 at 10:21:44AM +0200, Jan Beulich wrote: > On 15.09.2023 09:43, 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 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. > > A data point from a new system I'm still in the process of setting up: The > ACPI reboot method, as used by Linux, unconditionally means a warm reboot. > The EFI method, otoh, properly distinguishes "reboot=warm" from our default > of explicitly requesting cold reboot. (Without taking the EFI path, I > assume our write to the relevant BDA location simply has no effect, for > this being a legacy BIOS thing, and the system apparently defaults to warm > reboot when using the ACPI method.)
This is unfortunate, but IMO not as worse as getting a #UD or any other fault while attempting a reboot. We can always force this system to use UEFI reboot, if that does work better than ACPI. > Clearly, as a secondary effect, this system adds to my personal experience > of so far EFI reboot consistently working on all x86 hardware I have (had) > direct access to. (That said, this is the first non-Intel system, which > likely biases my overall experience.) I can try to gather some data, I can at least tell you that the Intel NUC11TNHi7 TGL does also hit a fault when attempting UEFI reboot. The above crash was from a Dell PowerEdge R6625. I do recall seeing this with other boxes on the Citrix lab, but don't know the exact models. I'm quite sure other downstreams can provide similar feedback. I think it's clear now that using ResetSystem() when booted from UEFI is not mandated by the UEFI specification, so I still stand by this patch and think we should select the default reboot method that has the highest chance of succeeding. Thanks, Roger.
