When increasing the array size in memblock_double_array() and the slab
is not yet available, a call to memblock_find_in_range() is used to
reserve/allocate memory. However, the range returned may not have been
accepted, which can result in a crash when booting an SNP guest:

  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

Mitigate this by calling accept_memory() on the memory range returned
before the slab is available.

Prior to v6.12, the accept_memory() interface used a 'start' and 'end'
parameter instead of 'start' and 'size', therefore the accept_memory()
call must be adjusted to specify 'start + size' for 'end' when applying
to kernels prior to v6.12.

Cc: <stable@vger.kernel.org> # see patch description, needs adjustments for <= 6.11
Fixes: dcdfdd40fa82 ("mm: Add support for unaccepted memory")
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
 mm/memblock.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index 0a53db4d9f7b..30fa553e9634 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -457,7 +457,14 @@ static int __init_memblock memblock_double_array(struct memblock_type *type,
 				min(new_area_start, memblock.current_limit),
 				new_alloc_size, PAGE_SIZE);
 
-		new_array = addr ? __va(addr) : NULL;
+		if (addr) {
+			/* The memory may not have been accepted, yet. */
+			accept_memory(addr, new_alloc_size);
+
+			new_array = __va(addr);
+		} else {
+			new_array = NULL;
+		}
 	}
 	if (!addr) {
 		pr_err("memblock: Failed to double %s array from %ld to %ld entries !\n",

base-commit: fc96b232f8e7c0a6c282f47726b2ff6a5fb341d2
-- 
2.46.2

From: Mike Rapoport (Microsoft) <rppt@kernel.org>

On Thu, 08 May 2025 12:24:10 -0500, Tom Lendacky wrote:
> When increasing the array size in memblock_double_array() and the slab
> is not yet available, a call to memblock_find_in_range() is used to
> reserve/allocate memory. However, the range returned may not have been
> accepted, which can result in a crash when booting an SNP guest:
> 
>   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
> 
> [...]

Applied to fixes branch of memblock.git tree, thanks!

[1/1] memblock: Accept allocated memory before use in memblock_double_array()
      commit: da8bf5daa5e55a6af2b285ecda460d6454712ff4

tree: https://git.kernel.org/pub/scm/linux/kernel/git/rppt/memblock
branch: fixes

--
Sincerely yours,
Mike.