Messages in this thread Patch in this message | | | Subject | Re: [RFC] mm/gup.c: Updated return value of {get|pin}_user_pages_fast() | From | John Hubbard <> | Date | Tue, 5 May 2020 12:38:17 -0700 |
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On 2020-05-05 12:14, Souptick Joarder wrote: > Currently {get|pin}_user_pages_fast() have 3 return value 0, -errno > and no of pinned pages. The only case where these two functions will > return 0, is for nr_pages <= 0, which doesn't find a valid use case. > But if at all any, then a -ERRNO will be returned instead of 0, which > means {get|pin}_user_pages_fast() will have 2 return values -errno & > no of pinned pages. > > Update all the callers which deals with return value 0 accordingly.
Hmmm, seems a little shaky. In order to do this safely, I'd recommend first changing gup_fast/pup_fast so so that they return -EINVAL if the caller specified nr_pages==0, and of course auditing all callers, to ensure that this won't cause problems.
The gup.c documentation would also need updating in a couple of comment blocks, above get_user_pages_remote(), and __get_user_pages(), because those talk about a zero return value.
This might be practical without slowing down the existing code, because there is already a check in place, so just tweaking it like this (untested) won't change performance at all:
diff --git a/mm/gup.c b/mm/gup.c index 11fda538c9d9..708eed79ae29 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2787,7 +2787,7 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages, end = start + len;
if (end <= start) - return 0; + return -EINVAL; if (unlikely(!access_ok((void __user *)start, len))) return -EFAULT;
...although I might be missing some other things that need a similar change, so you should look carefully for yourself.
Once that change (and anything I missed) is in place, then you could go ahead and stop handling ret==0 cases at the call sites.
thanks, -- John Hubbard NVIDIA
> > Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com> > --- > arch/ia64/kernel/err_inject.c | 2 +- > drivers/platform/goldfish/goldfish_pipe.c | 2 +- > drivers/staging/gasket/gasket_page_table.c | 4 ++-- > drivers/tee/tee_shm.c | 2 +- > mm/gup.c | 6 +++--- > net/rds/rdma.c | 2 +- > 6 files changed, 9 insertions(+), 9 deletions(-) > > diff --git a/arch/ia64/kernel/err_inject.c b/arch/ia64/kernel/err_inject.c > index 8b5b8e6b..fd72218 100644 > --- a/arch/ia64/kernel/err_inject.c > +++ b/arch/ia64/kernel/err_inject.c > @@ -143,7 +143,7 @@ static DEVICE_ATTR(name, 0644, show_##name, store_##name) > int ret; > > ret = get_user_pages_fast(virt_addr, 1, FOLL_WRITE, NULL); > - if (ret<=0) { > + if (ret < 0) { > #ifdef ERR_INJ_DEBUG > printk("Virtual address %lx is not existing.\n",virt_addr); > #endif > diff --git a/drivers/platform/goldfish/goldfish_pipe.c b/drivers/platform/goldfish/goldfish_pipe.c > index 1ab207e..831449d 100644 > --- a/drivers/platform/goldfish/goldfish_pipe.c > +++ b/drivers/platform/goldfish/goldfish_pipe.c > @@ -277,7 +277,7 @@ static int goldfish_pin_pages(unsigned long first_page, > ret = pin_user_pages_fast(first_page, requested_pages, > !is_write ? FOLL_WRITE : 0, > pages); > - if (ret <= 0) > + if (ret < 0) > return -EFAULT; > if (ret < requested_pages) > *iter_last_page_size = PAGE_SIZE; > diff --git a/drivers/staging/gasket/gasket_page_table.c b/drivers/staging/gasket/gasket_page_table.c > index f6d7157..1d08e1d 100644 > --- a/drivers/staging/gasket/gasket_page_table.c > +++ b/drivers/staging/gasket/gasket_page_table.c > @@ -489,11 +489,11 @@ static int gasket_perform_mapping(struct gasket_page_table *pg_tbl, > ret = get_user_pages_fast(page_addr - offset, 1, > FOLL_WRITE, &page); > > - if (ret <= 0) { > + if (ret < 0) { > dev_err(pg_tbl->device, > "get user pages failed for addr=0x%lx, offset=0x%lx [ret=%d]\n", > page_addr, offset, ret); > - return ret ? ret : -ENOMEM; > + return ret; > } > ++pg_tbl->num_active_pages; > > diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c > index bd679b7..2706a1f 100644 > --- a/drivers/tee/tee_shm.c > +++ b/drivers/tee/tee_shm.c > @@ -230,7 +230,7 @@ struct tee_shm *tee_shm_register(struct tee_context *ctx, unsigned long addr, > if (rc > 0) > shm->num_pages = rc; > if (rc != num_pages) { > - if (rc >= 0) > + if (rc > 0) > rc = -ENOMEM; > ret = ERR_PTR(rc); > goto err; > diff --git a/mm/gup.c b/mm/gup.c > index 50681f0..8d293ed 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -2760,7 +2760,7 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages, > end = start + len; > > if (end <= start) > - return 0; > + return -EINVAL; > if (unlikely(!access_ok((void __user *)start, len))) > return -EFAULT; > > @@ -2805,8 +2805,8 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages, > * calling get_user_pages(). > * > * Returns number of pages pinned. This may be fewer than the number requested. > - * If nr_pages is 0 or negative, returns 0. If no pages were pinned, returns > - * -errno. > + * If nr_pages is 0 or negative, returns -errno. If no pages were pinned, > + * returns -errno. > */ > int get_user_pages_fast(unsigned long start, int nr_pages, > unsigned int gup_flags, struct page **pages) > diff --git a/net/rds/rdma.c b/net/rds/rdma.c > index a7ae118..44b96e6 100644 > --- a/net/rds/rdma.c > +++ b/net/rds/rdma.c > @@ -161,7 +161,7 @@ static int rds_pin_pages(unsigned long user_addr, unsigned int nr_pages, > gup_flags |= FOLL_WRITE; > > ret = pin_user_pages_fast(user_addr, nr_pages, gup_flags, pages); > - if (ret >= 0 && ret < nr_pages) { > + if (ret > 0 && ret < nr_pages) { > unpin_user_pages(pages, ret); > ret = -EFAULT; > } >
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