linux-kernel - [PATCH v3] fpga: dfl: afu: convert get_user_pages() --> pin_user

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Date:   Mon, 25 May 2020 15:17:54 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     LKML <linux-kernel@...r.kernel.org>
CC:     John Hubbard <jhubbard@...dia.com>, Xu Yilun <yilun.xu@...el.com>,
        Wu Hao <hao.wu@...el.com>, Moritz Fischer <mdf@...nel.org>,
        <linux-fpga@...r.kernel.org>
Subject: [PATCH v3] fpga: dfl: afu: convert get_user_pages() --> pin_user_pages()

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.xu@...el.com>
Cc: Wu Hao <hao.wu@...el.com>
Cc: Moritz Fischer <mdf@...nel.org>
Cc: linux-fpga@...r.kernel.org
Signed-off-by: John Hubbard <jhubbard@...dia.com>
---

Hi,

This is the same logical change as in v2, but it is applied to
char-misc-next, in order to avoid a merge problem with Souptick's
commit c9d7e3da1f3c ("fpga: dfl: afu: Corrected error handling levels <Souptick Joarder>")

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 5942343a5d6e..0b817b722920 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);
@@ -57,22 +48,22 @@ 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 free_pages;
 	} else if (pinned != npages) {
 		ret = -EFAULT;
-		goto put_pages;
+		goto unpin_pages;
 	}
 
 	dev_dbg(dev, "%d pages pinned\n", pinned);
 
 	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);
 
-- 
2.26.2