On 9/26/22 07:10, Kirill A. Shutemov wrote:

On Sat, Sep 24, 2022 at 04:03:02AM +0300, Kirill A. Shutemov wrote:

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On Thu, Sep 22, 2022 at 09:31:12AM -0500, Tom Lendacky wrote:

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On 9/8/22 14:28, Mike Rapoport wrote:

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On Thu, Sep 08, 2022 at 09:23:07AM -0700, Dionna Amalie Glaze wrote:

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Looks like the first access to the memory map fails, although I think
it's not in INIT_LIST_HEAD() but rather in init_page_count().

I'd start with making sure that page_alloc::memmap_alloc() actually returns
accepted memory. If you build kernel with CONFIG_DEBUG_VM=y the memory map
will poisoned in this function, so my guess is it'd crash there.

That's a wonderful hint, thank you! I did not run this test
CONFIG_DEBUG_VM set, but you think it's possible it could still be
here?

It depends on how you configured your kernel. Say, defconfig does not set
it.

I also hit the issue at 256GB. My config is using CONFIG_SPARSEMEM_VMEMMAP
and fails in memmap_init_range() when attempting to add the first PFN. It
looks like the underlying page that is backing the vmemmap has not been
accepted (I receive a #VC 0x404 => page not validated).

Kirill, is this a path that you've looked at? It would appear that somewhere
in the vmemmap_populate_hugepages() path, some memory acceptance needs to be
done for the pages that are used to back vmemmap. I'm not very familiar with
this code, so I'm not sure why everything works for a guest with 255GB of
memory, but then fails for a guest with 256GB of memory.

Hm. I don't have machine that large at hands at the moment. And I have not
looked at the codepath before.

I will try to look into the issue.

I'm not able to trigger the bug.

With help of vm.overcommit_memory=1, I was managed boot TDX guest to shell
with 256G and 1T of guest memory just fine.

Any chance it is SEV-SNP specific?

There's always a chance. I'll do some more tracing and see what I can find 
to try and be certain.

Or maybe there some difference in kernel config? Could you share yours?

Yes, I'll send that to you off-list.

Thanks,
Tom