[Intel-gfx] Patch "drm/i915: Don't use BAR mappings for ring buffers with LLC" has been added to the 5.4-stable tree

[gregkh at linuxfoundation.org]

This is a note to let you know that I've just added the patch titled

    drm/i915: Don't use BAR mappings for ring buffers with LLC

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     drm-i915-don-t-use-bar-mappings-for-ring-buffers-with-llc.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable at vger.kernel.org> know about it.


>From 85636167e3206c3fbd52254fc432991cc4e90194 Mon Sep 17 00:00:00 2001
From: John Harrison <John.C.Harrison at Intel.com>
Date: Wed, 15 Feb 2023 17:11:01 -0800
Subject: drm/i915: Don't use BAR mappings for ring buffers with LLC
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

From: John Harrison <John.C.Harrison at Intel.com>

commit 85636167e3206c3fbd52254fc432991cc4e90194 upstream.

Direction from hardware is that ring buffers should never be mapped
via the BAR on systems with LLC. There are too many caching pitfalls
due to the way BAR accesses are routed. So it is safest to just not
use it.

Signed-off-by: John Harrison <John.C.Harrison at Intel.com>
Fixes: 9d80841ea4c9 ("drm/i915: Allow ringbuffers to be bound anywhere")
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Cc: Jani Nikula <jani.nikula at linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
Cc: intel-gfx at lists.freedesktop.org
Cc: <stable at vger.kernel.org> # v4.9+
Tested-by: Jouni Högander <jouni.hogander at intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230216011101.1909009-3-John.C.Harrison@Intel.com
(cherry picked from commit 65c08339db1ada87afd6cfe7db8e60bb4851d919)
Signed-off-by: Jani Nikula <jani.nikula at intel.com>
Signed-off-by: John Harrison <John.C.Harrison at Intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
 drivers/gpu/drm/i915/gt/intel_ringbuffer.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/i915/gt/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/gt/intel_ringbuffer.c
@@ -1208,7 +1208,7 @@ int intel_ring_pin(struct intel_ring *ri
 	if (unlikely(ret))
 		goto err_unpin;
 
-	if (i915_vma_is_map_and_fenceable(vma))
+	if (i915_vma_is_map_and_fenceable(vma) && !HAS_LLC(vma->vm->i915))
 		addr = (void __force *)i915_vma_pin_iomap(vma);
 	else
 		addr = i915_gem_object_pin_map(vma->obj,
@@ -1252,7 +1252,7 @@ void intel_ring_unpin(struct intel_ring
 	intel_ring_reset(ring, ring->emit);
 
 	i915_vma_unset_ggtt_write(vma);
-	if (i915_vma_is_map_and_fenceable(vma))
+	if (i915_vma_is_map_and_fenceable(vma) && !HAS_LLC(vma->vm->i915))
 		i915_vma_unpin_iomap(vma);
 	else
 		i915_gem_object_unpin_map(vma->obj);


Patches currently in stable-queue which might be from John.C.Harrison at Intel.com are

queue-5.4/drm-i915-don-t-use-bar-mappings-for-ring-buffers-with-llc.patch