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

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Date:   Mon, 26 Sep 2022 08:38:34 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.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 9/26/22 07:10, Kirill A. Shutemov wrote:
> On Sat, Sep 24, 2022 at 04:03:02AM +0300, Kirill A. Shutemov wrote:
>> 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.
> 
> 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

>