Re: [PATCH 1/1] vfio/spapr_tce: convert get_user_pages() --> pin_user_pages()
On 2020-05-26 12:28, Souptick Joarder wrote: @@ -486,7 +486,7 @@ static int tce_iommu_use_page(unsigned long tce, unsigned long *hpa) struct page *page = NULL; enum dma_data_direction direction = iommu_tce_direction(tce); - if (get_user_pages_fast(tce & PAGE_MASK, 1, + if (pin_user_pages_fast(tce & PAGE_MASK, 1, direction != DMA_TO_DEVICE ? FOLL_WRITE : 0, ) != 1) return -EFAULT; There are few places where nr_pages is passed as 1 to get_user_pages_fast(). With similar conversion those will be changed to pin_user_pages_fast(). Does it make sense to add an inline like - pin_user_page_fast(), similar to get_user_page_fast_only() ( now merged in linux-next) ? Perhaps not *just* yet, IMHO. There are only two places so far: here, and dax_lock_page(). And we don't expect that many places, either, because pin_user_pages*(), unlike get_user_pages(), is more likely to operate on a bunch of pages at once. Although, that could change if we look into the remaining call sites and find more single-page cases that need a gup-to-pup conversion. get_user_pages*() has a few more situations (Case 4, in Documentation/core-api/pin_user_pages.rst: struct page manipulation) in which it operates on single pages. Those will remain get_user_pages*() calls, or perhaps change to get_user_page(). thanks, -- John Hubbard NVIDIA
Re: [PATCH 1/1] vfio/spapr_tce: convert get_user_pages() --> pin_user_pages()
Hi John, On Sat, May 23, 2020 at 7:13 AM John Hubbard 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*() + put_page() 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/ > > Cc: Alex Williamson > Cc: Cornelia Huck > Cc: k...@vger.kernel.org > Signed-off-by: John Hubbard > --- > > Hi, > > I'm compile-tested this, but am not able to run-time test, so any > testing help is much appreciated! > > thanks, > John Hubbard > NVIDIA > > drivers/vfio/vfio_iommu_spapr_tce.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c > b/drivers/vfio/vfio_iommu_spapr_tce.c > index 16b3adc508db..fe888b5dcc00 100644 > --- a/drivers/vfio/vfio_iommu_spapr_tce.c > +++ b/drivers/vfio/vfio_iommu_spapr_tce.c > @@ -383,7 +383,7 @@ static void tce_iommu_unuse_page(struct tce_container > *container, > struct page *page; > > page = pfn_to_page(hpa >> PAGE_SHIFT); > - put_page(page); > + unpin_user_page(page); > } > > static int tce_iommu_prereg_ua_to_hpa(struct tce_container *container, > @@ -486,7 +486,7 @@ static int tce_iommu_use_page(unsigned long tce, unsigned > long *hpa) > struct page *page = NULL; > enum dma_data_direction direction = iommu_tce_direction(tce); > > - if (get_user_pages_fast(tce & PAGE_MASK, 1, > + if (pin_user_pages_fast(tce & PAGE_MASK, 1, > direction != DMA_TO_DEVICE ? FOLL_WRITE : 0, > ) != 1) > return -EFAULT; There are few places where nr_pages is passed as 1 to get_user_pages_fast(). With similar conversion those will be changed to pin_user_pages_fast(). Does it make sense to add an inline like - pin_user_page_fast(), similar to get_user_page_fast_only() ( now merged in linux-next) ?
[PATCH 1/1] vfio/spapr_tce: convert get_user_pages() --> pin_user_pages()
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*() + put_page() 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/ Cc: Alex Williamson Cc: Cornelia Huck Cc: k...@vger.kernel.org Signed-off-by: John Hubbard --- Hi, I'm compile-tested this, but am not able to run-time test, so any testing help is much appreciated! thanks, John Hubbard NVIDIA drivers/vfio/vfio_iommu_spapr_tce.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c index 16b3adc508db..fe888b5dcc00 100644 --- a/drivers/vfio/vfio_iommu_spapr_tce.c +++ b/drivers/vfio/vfio_iommu_spapr_tce.c @@ -383,7 +383,7 @@ static void tce_iommu_unuse_page(struct tce_container *container, struct page *page; page = pfn_to_page(hpa >> PAGE_SHIFT); - put_page(page); + unpin_user_page(page); } static int tce_iommu_prereg_ua_to_hpa(struct tce_container *container, @@ -486,7 +486,7 @@ static int tce_iommu_use_page(unsigned long tce, unsigned long *hpa) struct page *page = NULL; enum dma_data_direction direction = iommu_tce_direction(tce); - if (get_user_pages_fast(tce & PAGE_MASK, 1, + if (pin_user_pages_fast(tce & PAGE_MASK, 1, direction != DMA_TO_DEVICE ? FOLL_WRITE : 0, ) != 1) return -EFAULT; -- 2.26.2
