linux-kernel - [patch V3 31/37] drm/ttm: Replace kmap

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Date:   Tue, 03 Nov 2020 10:27:43 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Linus Torvalds <torvalds@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Paul McKenney <paulmck@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Christian Koenig <christian.koenig@....com>,
        Huang Rui <ray.huang@....com>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Benjamin LaHaise <bcrl@...ck.org>,
        linux-fsdevel@...r.kernel.org, linux-aio@...ck.org,
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Subject: [patch V3 31/37] drm/ttm: Replace kmap_atomic() usage

There is no reason to disable pagefaults and preemption as a side effect of
kmap_atomic_prot().

Use kmap_local_page_prot() instead and document the reasoning for the
mapping usage with the given pgprot.

Remove the NULL pointer check for the map. These functions return a valid
address for valid pages and the return was bogus anyway as it would have
left preemption and pagefaults disabled.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Christian Koenig <christian.koenig@....com>
Cc: Huang Rui <ray.huang@....com>
Cc: David Airlie <airlied@...ux.ie>
Cc: Daniel Vetter <daniel@...ll.ch>
Cc: dri-devel@...ts.freedesktop.org
---
V3: New patch
---
 drivers/gpu/drm/ttm/ttm_bo_util.c |   20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

--- a/drivers/gpu/drm/ttm/ttm_bo_util.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
@@ -181,13 +181,15 @@ static int ttm_copy_io_ttm_page(struct t
 		return -ENOMEM;
 
 	src = (void *)((unsigned long)src + (page << PAGE_SHIFT));
-	dst = kmap_atomic_prot(d, prot);
-	if (!dst)
-		return -ENOMEM;
+	/*
+	 * Ensure that a highmem page is mapped with the correct
+	 * pgprot. For non highmem the mapping is already there.
+	 */
+	dst = kmap_local_page_prot(d, prot);
 
 	memcpy_fromio(dst, src, PAGE_SIZE);
 
-	kunmap_atomic(dst);
+	kunmap_local(dst);
 
 	return 0;
 }
@@ -203,13 +205,15 @@ static int ttm_copy_ttm_io_page(struct t
 		return -ENOMEM;
 
 	dst = (void *)((unsigned long)dst + (page << PAGE_SHIFT));
-	src = kmap_atomic_prot(s, prot);
-	if (!src)
-		return -ENOMEM;
+	/*
+	 * Ensure that a highmem page is mapped with the correct
+	 * pgprot. For non highmem the mapping is already there.
+	 */
+	src = kmap_local_page_prot(s, prot);
 
 	memcpy_toio(dst, src, PAGE_SIZE);
 
-	kunmap_atomic(src);
+	kunmap_local(src);
 
 	return 0;
 }