Re: [PATCH v2] fpga: dfl: afu: convert get_user_pages() --> pin_user_pages()

[John Hubbard]

On 2020-05-19 13:14, John Hubbard wrote:

This code was using get_user_pages_fast(), in a "Case 2" scenario
(DMA/RDMA), using the categorization from [1]. That means that it's
time to convert the get_user_pages_fast() + put_page() calls to
pin_user_pages_fast() + 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: Xu Yilun <yilun...@intel.com>
Cc: Wu Hao <hao...@intel.com>
Cc: Moritz Fischer <m...@kernel.org>
Cc: linux-f...@vger.kernel.org
Signed-off-by: John Hubbard <jhubb...@nvidia.com>

Hi Moritz and FPGA developers,

Is this OK? And if so, is it going into your git tree? Or should I
send it up through a different tree? (I'm new to the FPGA development
model).


thanks,
--
John Hubbard
NVIDIA

---

Hi,

Changes since v1:

Changed the label from "put_pages", to "unpin_pages".

thanks,
John Hubbard
NVIDIA

drivers/fpga/dfl-afu-dma-region.c | 19 +++++--------------

  1 file changed, 5 insertions(+), 14 deletions(-)

diff --git a/drivers/fpga/dfl-afu-dma-region.c 
b/drivers/fpga/dfl-afu-dma-region.c
index 62f924489db5..a31dd3a7e581 100644
--- a/drivers/fpga/dfl-afu-dma-region.c
+++ b/drivers/fpga/dfl-afu-dma-region.c
@@ -16,15 +16,6 @@

#include "dfl-afu.h" -static void put_all_pages(struct page **pages, int npages)

-{
-       int i;
-
-       for (i = 0; i < npages; i++)
-               if (pages[i])
-                       put_page(pages[i]);
-}
-
  void afu_dma_region_init(struct dfl_feature_platform_data *pdata)
  {
        struct dfl_afu *afu = dfl_fpga_pdata_get_private(pdata);
@@ -57,11 +48,11 @@ static int afu_dma_pin_pages(struct 
dfl_feature_platform_data *pdata,
                goto unlock_vm;
        }

- pinned = get_user_pages_fast(region->user_addr, npages, FOLL_WRITE,

+       pinned = pin_user_pages_fast(region->user_addr, npages, FOLL_WRITE,
                                     region->pages);
        if (pinned < 0) {
                ret = pinned;
-               goto put_pages;
+               goto unpin_pages;
        } else if (pinned != npages) {
                ret = -EFAULT;
                goto free_pages;
@@ -71,8 +62,8 @@ static int afu_dma_pin_pages(struct dfl_feature_platform_data 
*pdata,

return 0; -put_pages:

-       put_all_pages(region->pages, pinned);
+unpin_pages:
+       unpin_user_pages(region->pages, pinned);
  free_pages:
        kfree(region->pages);
  unlock_vm:
@@ -94,7 +85,7 @@ static void afu_dma_unpin_pages(struct 
dfl_feature_platform_data *pdata,
        long npages = region->length >> PAGE_SHIFT;
        struct device *dev = &pdata->dev->dev;

- put_all_pages(region->pages, npages);

+       unpin_user_pages(region->pages, npages);
        kfree(region->pages);
        account_locked_vm(current->mm, npages, false);