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

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Message-ID: <20220924010302.bwas4zbro37rrxai@box.shutemov.name>
Date:   Sat, 24 Sep 2022 04:03:02 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     Dionna Amalie Glaze <dionnaglaze@...gle.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Vlastimil Babka <vbabka@...e.cz>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joerg Roedel <jroedel@...e.de>,
        Ard Biesheuvel <ardb@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Dario Faggioli <dfaggioli@...e.com>,
        Mike Rapoport <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Marcelo Cerri <marcelo.cerri@...onical.com>,
        tim.gardner@...onical.com,
        Khalid ElMously <khalid.elmously@...onical.com>,
        philip.cox@...onical.com,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-coco@...ts.linux.dev, linux-efi <linux-efi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>
Subject: Re: [PATCHv7 02/14] mm: Add support for unaccepted memory

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