On Thu, May 28, 2020 at 12:37 AM John Hubbard <jhubb...@nvidia.com> wrote: > > On 2020-05-27 01:51, Daniel Vetter wrote: > > On Wed, May 27, 2020 at 10:48:52AM +0200, Daniel Vetter wrote: > >> On Tue, May 26, 2020 at 03:57:45PM -0700, John Hubbard wrote: > >>> On 2020-05-26 14:00, Souptick Joarder wrote: > >>>> This code was using get_user_pages(), in a "Case 2" scenario > >>>> (DMA/RDMA), using the categorization from [1]. That means that it's > >>>> time to convert the get_user_pages() + release_pages() calls to > >>>> pin_user_pages() + unpin_user_pages() calls. > >>>> > >>>> There is some helpful background in [2]: basically, this is a small > >>>> part of fixing a long-standing disconnect between pinning pages, and > >>>> file systems' use of those pages. > >>>> > >>>> [1] Documentation/core-api/pin_user_pages.rst > >>>> > >>>> [2] "Explicit pinning of user-space pages": > >>>> https://lwn.net/Articles/807108/ > >> > >> I don't think this is a case 2 here, nor is it any of the others. Feels > >> like not covered at all by the doc. > >> > >> radeon has a mmu notifier (might be a bit broken, but hey whatever there's > >> other drivers which have the same concept, but less broken). So when you > >> do an munmap, radeon will release the page refcount. > > > > Aha, thanks Daniel. I withdraw my misinformed ACK, then. > > > I forgot to add: It's also not case 3, since there's no hw page fault > > support. It's all faked in software, and explicitly synchronizes against > > pending io (or preempts it, that depends a bit upon the jobs running). > > > > This is what case 3 was *intended* to cover, but it looks like case 3 needs to > be written a little better. I'll attempt that, and Cc you on the actual patch > to -mm. (I think we also need a case 5 for an unrelated scenario, too, so > it's time.)
There were no *case 5* in the other patch posted in -mm. Do we need to add it ? > > > thanks, > -- > John Hubbard > NVIDIA > > > >> Which case it that? > >> > >> Note that currently only amdgpu doesn't work like that for gpu dma > >> directly to userspace ranges, it uses hmm and afaiui doens't hold a full > >> page pin refcount. > >> > >> Cheers, Daniel > >> > >> > >>>> > >>>> Signed-off-by: Souptick Joarder <jrdr.li...@gmail.com> > >>>> Cc: John Hubbard <jhubb...@nvidia.com> > >>>> > >>>> Hi, > >>>> > >>>> I'm compile tested this, but unable to run-time test, so any testing > >>>> help is much appriciated. > >>>> --- > >>>> drivers/gpu/drm/radeon/radeon_ttm.c | 6 +++--- > >>>> 1 file changed, 3 insertions(+), 3 deletions(-) > >>>> > >>>> diff --git a/drivers/gpu/drm/radeon/radeon_ttm.c > >>>> b/drivers/gpu/drm/radeon/radeon_ttm.c > >>>> index 5d50c9e..e927de2 100644 > >>>> --- a/drivers/gpu/drm/radeon/radeon_ttm.c > >>>> +++ b/drivers/gpu/drm/radeon/radeon_ttm.c > >>>> @@ -506,7 +506,7 @@ static int radeon_ttm_tt_pin_userptr(struct ttm_tt > >>>> *ttm) > >>>> uint64_t userptr = gtt->userptr + pinned * PAGE_SIZE; > >>>> struct page **pages = ttm->pages + pinned; > >>>> - r = get_user_pages(userptr, num_pages, write ? FOLL_WRITE : 0, > >>>> + r = pin_user_pages(userptr, num_pages, write ? FOLL_WRITE : 0, > >>>> pages, NULL); > >>>> if (r < 0) > >>>> goto release_pages; > >>>> @@ -535,7 +535,7 @@ static int radeon_ttm_tt_pin_userptr(struct ttm_tt > >>>> *ttm) > >>>> kfree(ttm->sg); > >>>> release_pages: > >>>> - release_pages(ttm->pages, pinned); > >>>> + unpin_user_pages(ttm->pages, pinned); > >>>> return r; > >>>> } > >>>> @@ -562,7 +562,7 @@ static void radeon_ttm_tt_unpin_userptr(struct > >>>> ttm_tt *ttm) > >>>> set_page_dirty(page); > >>> > >>> > >>> Maybe we also need a preceding patch, to fix the above? It should be > >>> set_page_dirty_lock(), rather than set_page_dirty(), unless I'm > >>> overlooking > >>> something (which is very possible!). > >>> > >>> Either way, from a tunnel vision perspective of changing gup to pup, this > >>> looks good to me, so > >>> > >>> Acked-by: John Hubbard <jhubb...@nvidia.com> > >>> > >>> > >>> thanks, > >>> -- > >>> John Hubbard > >>> NVIDIA > >>> > >>>> mark_page_accessed(page); > >>>> - put_page(page); > >>>> + unpin_user_page(page); > >>>> } > >>>> sg_free_table(ttm->sg); > >>>> > >>> > >> > >> -- > >> Daniel Vetter > >> Software Engineer, Intel Corporation > >> http://blog.ffwll.ch > > >
