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Date:   Mon, 26 Sep 2022 15:10:27 +0300
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc:     Tom Lendacky <thomas.lendacky@amd.com>,
        Dionna Amalie Glaze <dionnaglaze@google.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Vlastimil Babka <vbabka@suse.cz>,
        Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
        Sean Christopherson <seanjc@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Joerg Roedel <jroedel@suse.de>,
        Ard Biesheuvel <ardb@kernel.org>,
        Andi Kleen <ak@linux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Ingo Molnar <mingo@redhat.com>,
        Dario Faggioli <dfaggioli@suse.com>,
        Mike Rapoport <rppt@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Marcelo Cerri <marcelo.cerri@canonical.com>,
        tim.gardner@canonical.com,
        Khalid ElMously <khalid.elmously@canonical.com>,
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        LKML <linux-kernel@vger.kernel.org>,
        Mike Rapoport <rppt@linux.ibm.com>
Subject: Re: [PATCHv7 02/14] mm: Add support for unaccepted memory
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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?

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

-- 
  Kiryl Shutsemau / Kirill A. Shutemov