Re: [PATCHv2 1/4] block: bio-integrity: directly map user buffers

Keith Busch
2023-11-06T15:03:00Z

On Mon, Nov 06, 2023 at 11:18:03AM +0530, Kanchan Joshi wrote:
> On 10/27/2023 11:49 PM, Keith Busch wrote:
> > + for (i = 0; i < nr_vecs; i = j) {
> > + size_t size = min_t(size_t, bytes, PAGE_SIZE - offs);
> > + struct folio *folio = page_folio(pages[i]);
> > +
> > + bytes -= size;
> > + for (j = i + 1; j < nr_vecs; j++) {
> > + size_t next = min_t(size_t, PAGE_SIZE, bytes);
> > +
> > + if (page_folio(pages[j]) != folio ||
> > + pages[j] != pages[j - 1] + 1)
> > + break;
> > + unpin_user_page(pages[j]);
>
> Is this unpin correct here?

Should be. The pages are bound to the folio, so this doesn't really
unpin the user page. It just drops a reference, and the folio holds the
final reference to the contiguous pages, which is released on
completion. You can find the same idea in io_uring/rscs.c,
io_sqe_buffer_register().