Re: [PATCH] io_uring: take page references for NOMMU pbuf_ring mmaps

[Jens Axboe <axboe@kernel.dk>]

On 4/21/26 11:39 AM, Jens Axboe wrote:
> 
> On Tue, 21 Apr 2026 15:46:16 +0200, Greg Kroah-Hartman wrote:
>> Under !CONFIG_MMU, io_uring_get_unmapped_area() returns the kernel
>> virtual address of the io_mapped_region's backing pages directly;
>> the user's VMA aliases the kernel allocation. io_uring_mmap() then
>> just returns 0 -- it takes no page references.
>>
>> The CONFIG_MMU path uses vm_insert_pages(), which takes a reference on
>> each inserted page.  Those references are released when the VMA is torn
>> down (zap_pte_range -> put_page). io_free_region() -> release_pages()
>> drops the io_uring-side references, but the pages survive until munmap
>> drops the VMA-side references.
>>
>> [...]
> 
> Applied, thanks!
> 
> [1/1] io_uring: take page references for NOMMU pbuf_ring mmaps
>       commit: d9b7b3d9c5286a786c7fe8220c55a6e012088c2e

Actually, I take that back - what prevents the io_mmap_get_region()
in the newly added io_uring_nommu_vm_close() from getting the same
region that we initially referenced the pages from in the nommu
variant of io_uring_mmap()?

-- 
Jens Axboe