From cdabbde1ed262090bff45929e1f5c1153ba5003e Mon Sep 17 00:00:00 2001 From: "Fabio M. De Francesco" Date: Thu, 13 Oct 2022 23:07:14 +0200 Subject: [PATCH] drm/radeon: Replace kmap() with kmap_local_page() MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit The use of kmap() is being deprecated in favor of kmap_local_page(). There are two main problems with kmap(): (1) It comes with an overhead as the mapping space is restricted and protected by a global lock for synchronization and (2) it also requires global TLB invalidation when the kmap’s pool wraps and it might block when the mapping space is fully utilized until a slot becomes available. With kmap_local_page() the mappings are per thread, CPU local, can take page faults, and can be called from any context (including interrupts). It is faster than kmap() in kernels with HIGHMEM enabled. Furthermore, the tasks can be preempted and, when they are scheduled to run again, the kernel virtual addresses are restored and still valid. Therefore, replace kmap() with kmap_local_page() in radeon_ttm_gtt_read(). Cc: "Venkataramanan, Anirudh" Reviewed-by: Kees Cook Reviewed-by: Christian König Suggested-by: Ira Weiny Signed-off-by: Fabio M. De Francesco Signed-off-by: Alex Deucher --- drivers/gpu/drm/radeon/radeon_ttm.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/radeon/radeon_ttm.c b/drivers/gpu/drm/radeon/radeon_ttm.c index d33fec4..bdb4c0e 100644 --- a/drivers/gpu/drm/radeon/radeon_ttm.c +++ b/drivers/gpu/drm/radeon/radeon_ttm.c @@ -869,11 +869,11 @@ static ssize_t radeon_ttm_gtt_read(struct file *f, char __user *buf, page = rdev->gart.pages[p]; if (page) { - ptr = kmap(page); + ptr = kmap_local_page(page); ptr += off; r = copy_to_user(buf, ptr, cur_size); - kunmap(rdev->gart.pages[p]); + kunmap_local(ptr); } else r = clear_user(buf, cur_size); -- 2.7.4