Re: Linux 5.13+ as Xen dom0 crashes on Ryzen CPU (ucode loading related?)

[Juergen Gross]

On 13.09.21 14:50, Marek Marczykowski-Górecki wrote:
> Hi,
>
> Since 5.13, the Xen (PV) dom0 crashes on boot, before even printing the
> kernel version.
> Test environment:
>   - Xen 4.14.2
>   - AMD Ryzen 5 4500U (reported also on AMD Ryzen 7 4750U)
>   - Linux 5.13.13, confirmed also on 5.14
>
> The crash happens only if the initramfs has earlycpio with microcode.
> I don't have a serial console, but I've got a photo with crash message
> (from Xen, Linux doesn't managed to print anything):
> https://user-images.githubusercontent.com/726704/133084966-5038f37e-001b-4688-9f90-83d09be3dc2d.jpg
>
> Transcription of some of it:
>
>      mapping kernel into physical memory
>      about to get started
>      (XEN) Pagetable walk from ffffffff82810888:
>      (XEN)  L4[0x1ff] = 0000000332815067 0000000000002815
>      (XEN)  L3[0x1fe] = 0000000332816067 0000000000002816
>      (XEN)  L2[0x014] = 0000000334018067 0000000000004018
>      (XEN)  L1[0x010] = 0000000332810067 0000000000002810
>      (XEN) domain_crash_sync called from entry.S: fault at ffff82d04033e790 x86_64/entry.S#domain_crash_page_fault
>      (XEN) Domain 0 (vcpu#0) crashed on cpu#0:
>      (XEN) ----[ Xen-4.14.2  x86_64  debug=n  Not tainted ]----
>      (XEN) CPU:    0
>      (XEN) RIP:    e033:[<0000000000000000>]

The domain's run state seems to be completely clobbered.

Did you try to boot the kernel with "earlyprintk=xen" to get some idea
how far it progressed?

I could imagine that doing the early reservations after the call of
e820__memory_setup() is problematic, as Xen PV guests have a hook in
this function performing some rather extended actions.

I'm not sure the call of early_reserve_memory() can be moved just before
the e820__memory_setup() call. If this is possibel it should be done
IMO, if not then the reservations which have been at the start of
setup_arch() might need to go there again.


Juergen

> I've bisected it down to the commit a799c2bd29d19c565f37fa038b31a0a1d44d0e4d
>
>      x86/setup: Consolidate early memory reservations
>
>      The early reservations of memory areas used by the firmware, bootloader,
>      kernel text and data are spread over setup_arch(). Moreover, some of them
>      happen *after* memblock allocations, e.g trim_platform_memory_ranges() and
>      trim_low_memory_range() are called after reserve_real_mode() that allocates
>      memory.
>
>      There was no corruption of these memory regions because memblock always
>      allocates memory either from the end of memory (in top-down mode) or above
>      the kernel image (in bottom-up mode). However, the bottom up mode is going
>      to be updated to span the entire memory [1] to avoid limitations caused by
>      KASLR.
>
>      Consolidate early memory reservations in a dedicated function to improve
>      robustness against future changes. Having the early reservations in one
>      place also makes it clearer what memory must be reserved before memblock
>      allocations are allowed.
>
>      Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
>      Signed-off-by: Borislav Petkov <bp@xxxxxxx>
>      Reviewed-by: Baoquan He <bhe@xxxxxxxxxx>
>      Acked-by: Borislav Petkov <bp@xxxxxxx>
>      Acked-by: David Hildenbrand <david@xxxxxxxxxx>
>      Link: [1] https://lore.kernel.org/lkml/20201217201214.3414100-2-guro@xxxxxx
>      Link: https://lkml.kernel.org/r/20210302100406.22059-2-rppt@xxxxxxxxxx
>
> Since this seems to affect Xen boot only, I'm copying xen-devel too.
>
> Any ideas?

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