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.) 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.) Jan
