linux-kernel - Re: SNP guest crash in memblock with unaccepted memory

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Message-ID: <43o2gni2stscuwjfr2cyawn4ikcfhsroact6t7civ3ud3e6sgi@jizmzw7lpzvt>
Date: Wed, 30 Apr 2025 12:14:08 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Mike Rapoport <rppt@...nel.org>, David Hildenbrand <david@...hat.com>
Cc: Tom Lendacky <thomas.lendacky@....com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Vlastimil Babka <vbabka@...e.cz>, 
	Mel Gorman <mgorman@...hsingularity.net>, "Kalra, Ashish" <ashish.kalra@....com>, 
	Rick Edgecombe <rick.p.edgecombe@...el.com>, linux-mm@...ck.org, linux-coco@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, Michael Roth <michael.roth@....com>
Subject: Re: SNP guest crash in memblock with unaccepted memory

On Mon, Apr 28, 2025 at 04:04:50PM +0200, David Hildenbrand wrote:
> On 27.04.25 17:01, Tom Lendacky wrote:
> > Hi Kirill,
> > 
> > Every now and then I experience an SNP guest boot failure for accessing
> > memory that hasn't been accepted. I managed to get a back trace:
> > 
> >    RIP: 0010:memcpy_orig+0x68/0x130
> >    Code: ...
> >    RSP: 0000:ffffffff9cc03ce8 EFLAGS: 00010006
> >    RAX: ff11001ff83e5000 RBX: 0000000000000000 RCX: fffffffffffff000
> >    RDX: 0000000000000bc0 RSI: ffffffff9dba8860 RDI: ff11001ff83e5c00
> >    RBP: 0000000000002000 R08: 0000000000000000 R09: 0000000000002000
> >    R10: 000000207fffe000 R11: 0000040000000000 R12: ffffffff9d06ef78
> >    R13: ff11001ff83e5000 R14: ffffffff9dba7c60 R15: 0000000000000c00
> >    memblock_double_array+0xff/0x310
> >    memblock_add_range+0x1fb/0x2f0
> >    memblock_reserve+0x4f/0xa0
> >    memblock_alloc_range_nid+0xac/0x130
> >    memblock_alloc_internal+0x53/0xc0
> >    memblock_alloc_try_nid+0x3d/0xa0
> >    swiotlb_init_remap+0x149/0x2f0
> >    mem_init+0xb/0xb0
> >    mm_core_init+0x8f/0x350
> >    start_kernel+0x17e/0x5d0
> >    x86_64_start_reservations+0x14/0x30
> >    x86_64_start_kernel+0x92/0xa0
> >    secondary_startup_64_no_verify+0x194/0x19b
> > 
> > I don't know a lot about memblock, but it appears that it needs to
> > allocate more memory for it's regions array and returns a range of memory
> > that hasn't been accepted. When the memcpy() runs, the SNP guest gets a
> > #VC 0x404 because of this.
> > 
> > Do you think it is as simple as calling accept_memory() on the memory
> > range returned from memblock_find_in_range() in memblock_double_array()?
> 
> (not Kirill, but replying :) )
> 
> Yeah, we seem to be effectively allocating memory from memblock ("from
> ourselves") without considering that memory must be accepted first.
> 
> accept_memory() on the new memory (in case of !slab) should be the right
> thing to do.

Right, it should do the trick.

BTW, Mike, is there any other codepath where memblock allocates memory for
itself? We need to cover them too.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov