On 30.04.20 21:02, Christian Borntraeger wrote: > On 30.04.20 20:12, Christian Borntraeger wrote: >> >> >> On 29.04.20 18:07, Dave Hansen wrote: >>> On 4/28/20 3:50 PM, Claudio Imbrenda wrote: >>>> If a page is inaccesible and it is used for things like sendfile, then >>>> the content of the page is not always touched, and can be passed >>>> directly to a driver, causing issues. >>>> >>>> This patch fixes the issue by adding a call to arch_make_page_accessible >>>> in page_cache_pipe_buf_confirm; this fixes the issue. >>> >>> I spent about 5 minutes putting together a patch: >>> >>> https://sr71.net/~dave/intel/accessible.patch >> >> You only set the page flag for compound pages. that of course leaves a big pile >> of pages marked a not accessible, thus explaining the sendto trace and all kind >> of other random traces. >> >> >> What do you see when you also do the SetPageAccessible(page); >> in the else page of prep_new_page (order == 0). >> (I do get > 10000 of these non compound page allocs just during boot). >> > > And yes, I think you are right that we should call the callback also for !FOLL_PIN. Thinking again about this I am no longer sure. Adding John Hubbard. Documentation/core-api/pin_user_pages.rst says: -------snip---------- Another way of thinking about these flags is as a progression of restrictions: FOLL_GET is for struct page manipulation, without affecting the data that the struct page refers to. FOLL_PIN is a *replacement* for FOLL_GET, and is for short term pins on pages whose data *will* get accessed. As such, FOLL_PIN is a "more severe" form of pinning. And finally, FOLL_LONGTERM is an even more restrictive case that has FOLL_PIN as a prerequisite: this is for pages that will be pinned longterm, and whose data will be accessed. -------snip---------- So John,is it ok to give a page to an I/O device where the code has used gup with FOLL_GET (or gup fast without pup) or would you consider this a bug?
