Messages in this thread | | | Subject | Re: [PATCH] drm/radeon: Convert get_user_pages() --> pin_user_pages() | From | John Hubbard <> | Date | Wed, 27 May 2020 12:07:08 -0700 |
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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.)
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.linux@gmail.com> >>>> Cc: John Hubbard <jhubbard@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 <jhubbard@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 >
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