Re: [PATCH 0/4] xen/arm: Unbreak ACPI

[Alex Bennée <alex.bennee@xxxxxxxxxx>]

Julien Grall <julien@xxxxxxx> writes:

> Hi Alex,
>
> On 29/09/2020 22:11, Alex Bennée wrote:
>> 
>> Julien Grall <julien@xxxxxxx> writes:
>> 
>>> Hi Alex,
>>>
>>> On 29/09/2020 16:29, Alex Bennée wrote:
>>>>
>>>> Julien Grall <julien@xxxxxxx> writes:
>>>>
>>>>> From: Julien Grall <jgrall@xxxxxxxxxx>
>>>>>
>>>>> Hi all,
>>>>>
>>>>> Xen on ARM has been broken for quite a while on ACPI systems. This
>>>>> series aims to fix it.
>>>>>
>>>>> Unfortunately I don't have a system with ACPI v6.0 or later (QEMU seems
>>>>> to only support 5.1). So I did only some light testing.
>>>>
>>>> I was hoping to get more diagnostics out to get it working under QEMU
>>>> TCG so I think must of missed a step:
>>>>
>>>>     Loading Xen 4.15-unstable ...
>>>>     Loading Linux 4.19.0-11-arm64 ...
>>>>     Loading initial ramdisk ...
>>>>     Using modules provided by bootloader in FDT
>>>>     Xen 4.15-unstable (c/s Sat Sep 26 21:55:42 2020 +0100 git:72f3d495d0) 
>>>> EFI loader
>>>>     ...silence...
>>>>
>>>> I have a grub installed from testing on a buster base:
>>>>
>>>>     dpkg --status grub-arm64-efi
>>>>     Version: 2.04-8
>>>>
>>>> With:
>>>>
>>>>     GRUB_CMDLINE_LINUX_DEFAULT=""
>>>>     GRUB_CMDLINE_LINUX="console=ttyAMA0"
>>>>     GRUB_CMDLINE_LINUX_XEN_REPLACE="console=hvc0 earlyprintk=xen"
>>>>     GRUB_CMDLINE_XEN="loglvl=all guest_loglvl=all 
>>>> com1=115200,8n1,0x3e8,5console=com1,vg"
>>>>
>>>> And I built Xen with --enable-systemd and tweaked the hypervisor .config:
>>>>
>>>>     CONFIG_EXPERT=y
>>>>     CONFIG_ACPI=y
>>>>
>>>> So any pointers to make it more verbose would be helpful.
>>>
>>> The error is hapenning before Xen setup the console. You can get early
>>> output on QEMU if you rebuild Xen with the following .config options:
>>>
>>> CONFIG_DEBUG=y
>>> CONFIG_EARLY_UART_CHOICE_PL011=y
>>> CONFIG_EARLY_UART_PL011=y
>>> CONFIG_EARLY_PRINTK=y
>>> CONFIG_EARLY_UART_BASE_ADDRESS=0x09000000
>>> CONFIG_EARLY_UART_PL011_BAUD_RATE=0
>>> CONFIG_EARLY_PRINTK_INC="debug-pl011.inc"
>> 
>> OK I can see it fails on the ACPI and then tries to fall back to FDT and
>> then fails to find the GIC:
>> 
>>    (XEN) CMDLINE[00000000f7bbe000]:chosen placeholder 
>> root=UUID=cf00cd3a-066b-4146-bedf-f811d3343077 ro console=hvc0 
>> earlyprintk=xen
>>    (XEN)
>>    (XEN) Command line: placeholder loglvl=all guest_loglvl=all 
>> com1=115200,8n1,0x3e8,5console=com1,vg no-real-mode edd=off
>>    (XEN) parameter "placeholder" unknown!
>>    (XEN) parameter "no-real-mode" unknown!
>>    (XEN) parameter "edd" unknown!
>>    (XEN) ACPI: RSDP 138560000, 0024 (r2 BOCHS )
>>    (XEN) ACPI: XSDT 138550000, 004C (r1 BOCHS  BXPCFACP        1       
>> 1000013)
>>    (XEN) ACPI: FACP 138510000, 010C (r5 BOCHS  BXPCFACP        1 BXPC        
>> 1)
>>    (XEN) ACPI: DSDT 138520000, 14A6 (r2 BOCHS  BXPCDSDT        1 BXPC        
>> 1)
>>    (XEN) ACPI: APIC 138500000, 018C (r3 BOCHS  BXPCAPIC        1 BXPC        
>> 1)
>>    (XEN) ACPI: GTDT 1384F0000, 0060 (r2 BOCHS  BXPCGTDT        1 BXPC        
>> 1)
>>    (XEN) ACPI: MCFG 1384E0000, 003C (r1 BOCHS  BXPCMCFG        1 BXPC        
>> 1)
>>    (XEN) ACPI: SPCR 1384D0000, 0050 (r2 BOCHS  BXPCSPCR        1 BXPC        
>> 1)
>>    (XEN) Unsupported FADT revision 5.1, should be 6.0+, will disable ACPI
>>    (XEN) acpi_boot_table_init: FADT not found (-22)
>>    (XEN) Domain heap initialised
>>    (XEN) Booting using Device Tree
>>    (XEN) Platform: Generic System
>>    (XEN)
>>    (XEN) ****************************************
>>    (XEN) Panic on CPU 0:
>>    (XEN) Unable to find compatible GIC in the device tree
>>    (XEN) ****************************************
>>    (XEN)
>>    (XEN) Reboot in five seconds...
>> 
>> Despite saying it is going to reboot it never manages to. Any idea how
>> it is trying to reset the system?
>
> This is a bit of chicken and eggs problem. To know the reset method, you 
> need to parse the ACPI tables. As we can't parse then we don't know the 
> reset method. So, Xen will just do an infinite loop.

Well you do get some ACPI tables - downgrading the minimum at least
restores the reset method detection. I wonder if it would be worth
defaulting to PSCI if you don't know rather than hang indefinitely?

FWIW the failure after that is failing to find the GIC - I'm just
looking at the MADT table parsing now. Why am I getting a sense of
DejaVu?

> It would probably be good to be more forthcoming with the users and say 
> it will not reboot.
>
> Also, IIRC, the time subsystem is not yet initialized. So it might be 
> possible to mdelay() doesn't work properly.

Surely that's an architectural subsystem so there is no reason that
couldn't be up and running.

>
> Cheers,


-- 
Alex Bennée