Re: [PATCH] physmem: fix qemu_ram_alloc_from_fd size calculation

[Steven Sistare <steven.sistare@oracle.com>]

On 1/2/2025 4:14 PM, Peter Xu wrote:
> On Thu, Jan 02, 2025 at 12:34:50PM -0800, Steve Sistare wrote:
>> qemu_ram_alloc_from_fd allocates space if file_size == 0.  If non-zero,
>> it uses the existing space and verifies it is large enough, but the
>> verification was broken when the offset parameter was introduced.  As
>> a result, a file smaller than offset passes the verification and causes
>> errors later.  Fix that, and update the error message to include offset.
>>
>> Peter provides this concise reproducer:
>>
>>    $ touch ramfile
>>    $ truncate -s 64M ramfile
>>    $ ./qemu-system-x86_64 -object memory-backend-file,mem-path=./ramfile,offset=128M,size=128M,id=mem1,prealloc=on
>>    qemu-system-x86_64: qemu_prealloc_mem: preallocating memory failed: Bad address
>>
>> With the fix, the error message is:
>>    qemu-system-x86_64: mem1 backing store size 0x4000000 is too small for 'size' option 0x8000000 plus 'offset' option 0x8000000
>>
> 
> Can have the cc tag here too to be super clear:
> 
> Cc: qemu-stable@nongnu.org

Done and resubmitted.

>> Fixes: 4b870dc4d0c0 ("hostmem-file: add offset option")
>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> 
> Reviewed-by: Peter Xu <peterx@redhat.com>
> 
> Please also feel free to attach this patch as the 1st patch when repost
> cpr-transfer, it could make dependency easier no matter how this would
> land.

Will do - steve

> Maybe it'll be still easier to go via a migration pull that collects cpr
> transfer as a whole. May depend on whether there'll be a memory API pull
> before that..