Re: [PATCHv7 02/14] mm: Add support for unaccepted memory

Kirill A. Shutemov
2022-09-24T01:03:12Z

On Thu, Sep 22, 2022 at 09:31:12AM -0500, Tom Lendacky wrote:
> On 9/8/22 14:28, Mike Rapoport wrote:
> > On Thu, Sep 08, 2022 at 09:23:07AM -0700, Dionna Amalie Glaze wrote:
> > > >
> > > > 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.

--
Kiryl Shutsemau / Kirill A. Shutemov