linux-kernel - [PATCH] staging: gasket: Convert get_user_pages*() --> pin_user

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Date:   Thu, 28 May 2020 02:32:42 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     rspringer@...gle.com, toddpoynor@...gle.com, benchan@...omium.org,
        gregkh@...uxfoundation.org
Cc:     devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        Souptick Joarder <jrdr.linux@...il.com>,
        John Hubbard <jhubbard@...dia.com>
Subject: [PATCH] staging: gasket: 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_page() 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/

Signed-off-by: Souptick Joarder <jrdr.linux@...il.com>
Cc: John Hubbard <jhubbard@...dia.com>

Hi,

I'm compile tested this, but unable to run-time test, so any testing
help is much appriciated.
---
 drivers/staging/gasket/gasket_page_table.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/gasket/gasket_page_table.c b/drivers/staging/gasket/gasket_page_table.c
index f6d7157..d712ad4 100644
--- a/drivers/staging/gasket/gasket_page_table.c
+++ b/drivers/staging/gasket/gasket_page_table.c
@@ -449,7 +449,7 @@ static bool gasket_release_page(struct page *page)
 
 	if (!PageReserved(page))
 		SetPageDirty(page);
-	put_page(page);
+	unpin_user_page(page);
 
 	return true;
 }
@@ -486,12 +486,12 @@ static int gasket_perform_mapping(struct gasket_page_table *pg_tbl,
 			ptes[i].dma_addr = pg_tbl->coherent_pages[0].paddr +
 					   off + i * PAGE_SIZE;
 		} else {
-			ret = get_user_pages_fast(page_addr - offset, 1,
+			ret = pin_user_pages_fast(page_addr - offset, 1,
 						  FOLL_WRITE, &page);
 
 			if (ret <= 0) {
 				dev_err(pg_tbl->device,
-					"get user pages failed for addr=0x%lx, offset=0x%lx [ret=%d]\n",
+					"pin user pages failed for addr=0x%lx, offset=0x%lx [ret=%d]\n",
 					page_addr, offset, ret);
 				return ret ? ret : -ENOMEM;
 			}
-- 
1.9.1