Re: What's missing for arm64 Xen boot with FDT via Grub in Debian Bullseye?

["Alex Bennée" <alex.bennee@linaro.org>]

Julien Grall <julien@xen.org> writes:

> On 28/05/2021 13:49, Alex Bennée wrote:
>> Hi,
>
> Hi Alex,
>
>> I'm currently trying to pull together the threads for booting Xen on
>> Debian. I'm currently doing this within QEMU's TCG emulation and the
>> "virt" machine model:
>>    -machine type=virt,virtualization=on,gic-version=3 \
>>    -cpu max,pauth-impdef=on
>> with the firmware on my Ubuntu machine:
>>    -drive
>> if=pflash,file=/usr/share/AAVMF/AAVMF_CODE.fd,format=raw,readonly=on
>> -drive if=pflash,file=$HOME/images/AAVMF_VARS.fd,format=raw
>> (qemu-efi-aarch64 Version: 0~20180205.c0d9813c-2ubuntu0.3)
>> When booting this way I get the Grub menu and Xen is loaded by Grub
>> but
>> falls over later:
>>    (XEN) MODULE[0]: 00000000f5869000 - 00000000f59b60c8 Xen
>>    (XEN) MODULE[1]: 000000013857d000 - 0000000138580000 Device Tree
>>    (XEN) MODULE[2]: 00000000f73a1000 - 00000000f8da0780 Kernel
>>    (XEN) MODULE[3]: 00000000f59b7000 - 00000000f739f99b Ramdisk
>>    (XEN)
>>    (XEN) CMDLINE[00000000f73a1000]:chosen placeholder root=UUID=435201aa-c5cf-4e7a-8107-5eef28844188 ro console=hvc0
>>    (XEN)
>>    (XEN) Command line: placeholder dom0_mem=2G loglvl=all guest_loglvl=all no-real-mode edd=off
>>    (XEN) parameter "placeholder" unknown!
>>    (XEN) parameter "no-real-mode" unknown!
>>    (XEN) parameter "edd" unknown!
>>    (XEN) Domain heap initialised
>>    (XEN) Booting using Device Tree
>>    (XEN) Platform: Generic System
>>    (XEN)
>>    (XEN) ****************************************
>>    (XEN) Panic on CPU 0:
>>    (XEN) Unable to find a compatible timer in the device tree
>>    (XEN) ****************************************
>> It seems like there are bits of the DT missing. I can however
>> successfully boot Xen with the Linux guest using the guest-loader device
>> and bypassing the firmware/boot code step. This gives:
>>    (XEN) MODULE[0]: 0000000040200000 - 000000004034d0c8 Xen
>>    (XEN) MODULE[1]: 0000000048000000 - 0000000048100000 Device Tree
>>    (XEN) MODULE[2]: 0000000046000000 - 0000000046eb2200 Kernel
>>    (XEN)
>>    (XEN) CMDLINE[0000000046000000]:chosen root=/dev/sda2 console=hvc0 earlyprintk=xen
>>    (XEN)
>>    (XEN) Command line: dom0_mem=4G dom0_max_vcpus=4
>>    (XEN) Domain heap initialised
>>    (XEN) Booting using Device Tree
>>    (XEN) Platform: Generic System
>>    (XEN) Taking dtuart configuration from /chosen/stdout-path
>>    (XEN) Looking for dtuart at "/pl011@9000000", options ""
>>     Xen 4.15.1-pre
>>    (XEN) Xen version 4.15.1-pre (alex.bennee@) (aarch64-linux-gnu-gcc (Debian 8.3.0-2) 8.3.0) debug=y Tue May 18 09:34:55 UTC 2021
>>    (XEN) Latest ChangeSet:
>>    (XEN) build-id: a50d8f03a1a15662ac7c4e5f73f2f544a6739df2
>>    (XEN) Processor: 411fd070: "ARM Limited", variant: 0x1, part 0xd07, rev 0x0
>>    (XEN) 64-bit Execution:
>>    (XEN)   Processor Features: 0000000001000222 0000000000000000
>>    (XEN)     Exception Levels: EL3:No EL2:64+32 EL1:64+32 EL0:64+32
>>    (XEN)     Extensions: FloatingPoint AdvancedSIMD GICv3-SysReg
>>    (XEN)   Debug Features: 0000000010305106 0000000000000000
>>    (XEN)   Auxiliary Features: 0000000000000000 0000000000000000
>>    (XEN)   Memory Model Features: 0000000000001124 0000000000000000
>>    (XEN)   ISA Features:  0000000000011120 0000000000000000
>>    (XEN) 32-bit Execution:
>>    (XEN)   Processor Features: 00000131:10011001
>>    (XEN)     Instruction Sets: AArch32 A32 Thumb Thumb-2 Jazelle
>>    (XEN)     Extensions: GenericTimer
>>    (XEN)   Debug Features: 03010066
>>    (XEN)   Auxiliary Features: 00000000
>>    (XEN)   Memory Model Features: 10101105 40000000 01260000 02102211
>>    (XEN)  ISA Features: 02101110 13112111 21232042 01112131 00011142 00011121
>>    (XEN) Using SMC Calling Convention v1.0
>>    (XEN) Using PSCI v0.2
>>    (XEN) SMP: Allowing 8 CPUs
>>    (XEN) enabled workaround for: ARM erratum 832075
>>    (XEN) enabled workaround for: ARM erratum 834220
>>    (XEN) enabled workaround for: ARM erratum 1319367
>>    (XEN) Generic Timer IRQ: phys=30 hyp=26 virt=27 Freq: 62500 KHz
>>    (XEN) GICv3 initialization:
>>    (XEN)       gic_dist_addr=0x00000008000000
>>    (XEN)       gic_maintenance_irq=25
>>    (XEN)       gic_rdist_stride=0
>>    (XEN)       gic_rdist_regions=1
>>    (XEN)       redistributor regions:
>>    (XEN)         - region 0: 0x000000080a0000 - 0x00000009000000
>>    (XEN) GICv3: 256 lines, (IID 0000043b).
>>    (XEN) GICv3: CPU0: Found redistributor in region 0 @000000004001c000
>> Attempting to boot with acpi=on still sees Grub attempt to use DT to
>> boot the hypervisor. However selecting the kernel directly boots with
>> ACPI (which is a shame as I'd like to see what FDT it gets presented
>> with).
>
> ACPI is not built by default in Xen on Arm. You will need to select it
> from Kconfig and rebuild the hypervisor.

OK so I think what was happening is grub was always passing ACPI and
with Xen not built for it there was simply no DTB to process. Testing
with a ACPI build works for Bullseye.

Testing on Buster Xen does boot but hangs at:

  (XEN) *** LOADING DOMAIN 0 ***
  (XEN) Loading d0 kernel from boot module @ 00000000f7d2d000
  (XEN) Loading ramdisk from boot module @ 00000000f304b000
  (XEN) Allocating 1:1 mappings totalling 2048MB for dom0:
  (XEN) BANK[0] 0x00000040000000-0x000000c0000000 (2048MB)
  (XEN) Grant table range: 0x000000f2ef5000-0x000000f2f35000
  (XEN) Allocating PPI 16 for event channel interrupt
  (XEN) Loading zImage from 00000000f7d2d000 to 0000000040080000-0000000041264780
  (XEN) Loading d0 initrd from 00000000f304b000 to 0x0000000048200000-0x000000004cee0c00
  (XEN) Loading d0 DTB to 0x0000000048000000-0x000000004800027f
  (XEN) Initial low memory virq threshold set at 0x4000 pages.
  (XEN) Scrubbing Free RAM in background
  (XEN) Std. Loglevel: All
  (XEN) Guest Loglevel: All
  (XEN) *** Serial input to DOM0 (type 'CTRL-a' three times to switch input)
  (XEN) Freed 380kB init memory.


I'll need to update by build environment and rebuild for Bullseye to
check I can still start a new domain.

>
>> The full command line for booting via the guest-loader is:
>>    ./qemu-system-aarch64 \
>>      -machine virt,virtualization=on,gic-version=3 \
>>      -cpu max,pauth-impdef=on \
>>      -serial mon:stdio \
>>      -netdev user,id=net1,hostfwd=tcp::2222-:22 \
>>      -device virtio-net-pci,netdev=net1 \
>>      -device virtio-scsi-pci \
>>      -drive file=/dev/zvol/hackpool-0/debian-buster-arm64,id=hd0,index=0,if=none,format=raw \
>>      -device scsi-hd,drive=hd0 \
>>      -display none \
>>      -m 16384 \
>>      -kernel ~/lsrc/xen/xen.build.arm64-xen/xen/xen \
>>      -append "dom0_mem=4G dom0_max_vcpus=4" \
>>      -device guest-loader,addr=0x46000000,kernel=$HOME/lsrc/linux.git/builds/arm64/arch/arm64/boot/Image,bootargs="root=/dev/sda2 console=hvc0 earlyprintk=xen" \
>>      -smp 8
>> So some questions:
>>    - is Xen on arm64 tested on Debian Bullseye? If so what platform?
>
> I am using Debian Bullseye on QEMU and also the FVP. We are also using
> Debian in Osstest for all the testing (it is possible an older version
> of Debian).
>
>>    - how do I tell Grub to do a straight FDT boot with the DT from the firmware?
>
> Is the firmware actually providing a DT? You could try to boot Xen
> from UEFI directly to confirm that.
>
> However, I vaguely recall that GRUB may only pass ACPI if it is provided.
>
>>    - are there any missing pieces I should be aware of?
>
> Other than re-building Xen with ACPI=y, I am not aware of any issue to
> use Xen with Debian bullseye.
>
> Cheers,


-- 
Alex Bennée