linux-kernel - [PATCH v2 9/9] drm/i915: Use kmap_local_page() in gem/i915_gem

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Message-Id: <20230329073220.3982460-10-zhao1.liu@linux.intel.com>
Date:   Wed, 29 Mar 2023 15:32:20 +0800
From:   Zhao Liu <zhao1.liu@...ux.intel.com>
To:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Matthew Auld <matthew.auld@...el.com>,
        Thomas Hellström 
        <thomas.hellstrom@...ux.intel.com>,
        Nirmoy Das <nirmoy.das@...el.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Christian König <christian.koenig@....com>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Cc:     Ira Weiny <ira.weiny@...el.com>,
        "Fabio M . De Francesco" <fmdefrancesco@...il.com>,
        Zhenyu Wang <zhenyu.z.wang@...el.com>,
        Zhao Liu <zhao1.liu@...el.com>
Subject: [PATCH v2 9/9] drm/i915: Use kmap_local_page() in gem/i915_gem_execbuffer.c

From: Zhao Liu <zhao1.liu@...el.com>

The use of kmap_atomic() is being deprecated in favor of
kmap_local_page()[1], and this patch converts the calls from
kmap_atomic() to kmap_local_page().

The main difference between atomic and local mappings is that local
mappings doesn't disable page faults or preemption (the preemption is
disabled for !PREEMPT_RT case, otherwise it only disables migration).

With kmap_local_page(), we can avoid the often unwanted side effect of
unnecessary page faults and preemption disables.

In i915_gem_execbuffer.c, eb->reloc_cache.vaddr is mapped by
kmap_atomic() in eb_relocate_entry(), and is unmapped by
kunmap_atomic() in reloc_cache_reset().

And this mapping/unmapping occurs in two places: one is in
eb_relocate_vma(), and another is in eb_relocate_vma_slow().

The function eb_relocate_vma() or eb_relocate_vma_slow() doesn't
need to disable pagefaults and preemption during the above mapping/
unmapping.

So it can simply use kmap_local_page() / kunmap_local() that can
instead do the mapping / unmapping regardless of the context.

Convert the calls of kmap_atomic() / kunmap_atomic() to
kmap_local_page() / kunmap_local().

[1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com

v2: No code change since v1. Added description of the motivation of
    using kmap_local_page() and "Suggested-by" tag of Fabio.

Suggested-by: Ira Weiny <ira.weiny@...el.com>
Suggested-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
Signed-off-by: Zhao Liu <zhao1.liu@...el.com>
---
Suggested by credits:
  Ira: Referred to his task document, review comments.
  Fabio: Referred to his boiler plate commit message and his description
         about why kmap_local_page() should be preferred.
---
 drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index 9dce2957b4e5..805565edd148 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -1151,7 +1151,7 @@ static void reloc_cache_unmap(struct reloc_cache *cache)
 
 	vaddr = unmask_page(cache->vaddr);
 	if (cache->vaddr & KMAP)
-		kunmap_atomic(vaddr);
+		kunmap_local(vaddr);
 	else
 		io_mapping_unmap_atomic((void __iomem *)vaddr);
 }
@@ -1167,7 +1167,7 @@ static void reloc_cache_remap(struct reloc_cache *cache,
 	if (cache->vaddr & KMAP) {
 		struct page *page = i915_gem_object_get_page(obj, cache->page);
 
-		vaddr = kmap_atomic(page);
+		vaddr = kmap_local_page(page);
 		cache->vaddr = unmask_flags(cache->vaddr) |
 			(unsigned long)vaddr;
 	} else {
@@ -1197,7 +1197,7 @@ static void reloc_cache_reset(struct reloc_cache *cache, struct i915_execbuffer
 		if (cache->vaddr & CLFLUSH_AFTER)
 			mb();
 
-		kunmap_atomic(vaddr);
+		kunmap_local(vaddr);
 		i915_gem_object_finish_access(obj);
 	} else {
 		struct i915_ggtt *ggtt = cache_to_ggtt(cache);
@@ -1229,7 +1229,7 @@ static void *reloc_kmap(struct drm_i915_gem_object *obj,
 	struct page *page;
 
 	if (cache->vaddr) {
-		kunmap_atomic(unmask_page(cache->vaddr));
+		kunmap_local(unmask_page(cache->vaddr));
 	} else {
 		unsigned int flushes;
 		int err;
@@ -1251,7 +1251,7 @@ static void *reloc_kmap(struct drm_i915_gem_object *obj,
 	if (!obj->mm.dirty)
 		set_page_dirty(page);
 
-	vaddr = kmap_atomic(page);
+	vaddr = kmap_local_page(page);
 	cache->vaddr = unmask_flags(cache->vaddr) | (unsigned long)vaddr;
 	cache->page = pageno;
 
-- 
2.34.1