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SubjectRe: Linux 5.13+ as Xen dom0 crashes on Ryzen CPU (ucode loading related?)
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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@linux.ibm.com>
> Signed-off-by: Borislav Petkov <bp@suse.de>
> Reviewed-by: Baoquan He <bhe@redhat.com>
> Acked-by: Borislav Petkov <bp@suse.de>
> Acked-by: David Hildenbrand <david@redhat.com>
> Link: [1] https://lore.kernel.org/lkml/20201217201214.3414100-2-guro@fb.com
> Link: https://lkml.kernel.org/r/20210302100406.22059-2-rppt@kernel.org
>
> Since this seems to affect Xen boot only, I'm copying xen-devel too.
>
> Any ideas?
>

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