[PATCH] drm: Explicitly compute the last cacheline for clflush on range

From: Chris Wilson <chris@chris-wilson.co.uk>
To: intel-gfx@lists.freedesktop.org
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>, dri-devel@lists.freedesktop.org
Subject: [PATCH] drm: Explicitly compute the last cacheline for clflush on range
Date: Fri, 16 Oct 2015 20:55:55 +0100	[thread overview]
Message-ID: <1445025355-19348-1-git-send-email-chris@chris-wilson.co.uk> (raw)

Fixes regression from

commit afcd950cafea6e27b739fe7772cbbeed37d05b8b
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Wed Jun 10 15:58:01 2015 +0100

    drm: Avoid the double clflush on the last cache line in drm_clflush_virt_range()

I'm stumped. Looking at the loop we should be iterating over every cache
line until we reach the start of the cacheline after the end of the
virtual range. Evidence says otherwise.

More bizarely, I stored the last address to be clflushed and found it to
be equal to the start of the cacheline containing the last byte. Doubly
purplexed.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92501
Testcase: gem_tiled_partial_pwrite_pread/reads
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/drm_cache.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_cache.c b/drivers/gpu/drm/drm_cache.c
index 6743ff7dccfa..7c909bc8b68a 100644
--- a/drivers/gpu/drm/drm_cache.c
+++ b/drivers/gpu/drm/drm_cache.c
@@ -131,10 +131,13 @@ drm_clflush_virt_range(void *addr, unsigned long length)
 #if defined(CONFIG_X86)
 	if (cpu_has_clflush) {
 		const int size = boot_cpu_data.x86_clflush_size;
-		void *end = addr + length;
-		addr = (void *)(((unsigned long)addr) & -size);
+		void *end;
+
+		end = (void *)(((unsigned long)addr + length - 1) & -size);
+		addr = (void *)((unsigned long)addr & -size);
+
 		mb();
-		for (; addr < end; addr += size)
+		for (; addr <= end; addr += size)
 			clflushopt(addr);
 		mb();
 		return;
-- 
2.6.1

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