[Xen-devel] Re: [PATCH] to fix ACPI slit table access at runtime

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 25.02.10 13:13 >>>
>By the way, a separate question for Jan: I notice you added an
>alloc_boot_pages() call in arch/x86/numa.c, and get a virtual address from
>mfn_to_virt(). This is bogus for x86_32, so can we just stub out that
>function for the 32-bit build: looks like the caller would then gracefully
>fail? I wonder whether this could explain the crash that Ian Jackson
>reported on one system with PAE Xen the other day.

Yes, quite possible. Although - specifically after his report - I ran
a 32-bit image on my only somewhat NUMA-ish system, and did not
see it die:

(XEN) SRAT: PXM 0 -> APIC 0 -> Node 0
(XEN) SRAT: PXM 0 -> APIC 1 -> Node 0
(XEN) SRAT: PXM 0 -> APIC 2 -> Node 0
(XEN) SRAT: PXM 0 -> APIC 3 -> Node 0
(XEN) SRAT: PXM 1 -> APIC 4 -> Node 1
(XEN) SRAT: PXM 1 -> APIC 5 -> Node 1
(XEN) SRAT: PXM 1 -> APIC 6 -> Node 1
(XEN) SRAT: PXM 1 -> APIC 7 -> Node 1
(XEN) SRAT: Node 0 PXM 0 0-a0000
(XEN) SRAT: Node 0 PXM 0 100000-80000000
(XEN) SRAT: Node 1 PXM 1 80000000-d0000000
(XEN) SRAT: Node 1 PXM 1 100000000-130000000
(XEN) NUMA: Allocated memnodemap from 2e37e000 - 2e380000
(XEN) NUMA: Using 8 for the hash shift.

All it took was the patch that's now c/s 20978. But indeed the
addresses printed suggest this cannot work properly, even if it
didn't crash.

Whether this indeed causes Ian's problems could be easily
clarified by him adding loglvl=all to see those two NUMA:
messages. What makes me think it may not is that CR2 was
zero in his log.

Removing the code for 32-bit altogether is certainly one option (in
that case I'd want to see _memnodemap to be reasonably
increased though, plus we should probably make an attempt to
reduce memnodemapsize again - the hash shift currently is unduly
small - and I have a patch for the original Linux code to do so).

All other options are likely indeed not worth it to make 32-bit
happy.

Jan


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