Re: SNP guest crash in memblock with unaccepted memory

[Tom Lendacky <thomas.lendacky@amd.com>]

On 4/28/25 09:04, 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.

Thanks, David. Let me add a call in for accept_memory in the !slab case
and see if that resolves it. May take a bit to repro, but should find
out eventually.

I'll submit a patch once I verify.

Thanks,
Tom

>