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

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Message-ID: <f12f5bd0-135b-91fd-9703-7df98500f9c5@amd.com>
Date: Sun, 27 Apr 2025 10:01:32 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Mike Rapoport
 <rppt@...nel.org>, David Hildenbrand <david@...hat.com>,
 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: SNP guest crash in memblock with unaccepted memory

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()?

Thanks,
Tom