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From:   Zhao Liu <zhao1.liu@linux.intel.com>
To:     Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Matthew Auld <matthew.auld@intel.com>,
        =?UTF-8?q?Thomas=20Hellstr=C3=B6m?= 
        <thomas.hellstrom@linux.intel.com>,
        Nirmoy Das <nirmoy.das@intel.com>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Chris Wilson <chris@chris-wilson.co.uk>,
        =?UTF-8?q?Christian=20K=C3=B6nig?= <christian.koenig@amd.com>,
        intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
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Cc:     Ira Weiny <ira.weiny@intel.com>,
        "Fabio M . De Francesco" <fmdefrancesco@gmail.com>,
        Zhenyu Wang <zhenyu.z.wang@intel.com>,
        Zhao Liu <zhao1.liu@intel.com>
Subject: [PATCH 3/9] drm/i915: Use kmap_local_page() in gem/i915_gem_shmem.c
Date:   Mon, 17 Oct 2022 17:37:19 +0800
Message-Id: <20221017093726.2070674-4-zhao1.liu@linux.intel.com>
In-Reply-To: <20221017093726.2070674-1-zhao1.liu@linux.intel.com>
References: <20221017093726.2070674-1-zhao1.liu@linux.intel.com>
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From: Zhao Liu <zhao1.liu@intel.com>

The use of kmap_atomic() is being deprecated in favor of
kmap_local_page()[1].

The main difference between atomic and local mappings is that local
mappings doesn't disable page faults or preemption.

In drm/i915/gem/i915_gem_shmem.c, the function shmem_pwrite() need to
disable pagefault to eliminate the potential recursion fault[2]. But
here __copy_from_user_inatomic() doesn't need to disable preemption and
local mapping is valid for sched in/out.

So it can use kmap_local_page() / kunmap_local() with
pagefault_disable() / pagefault_enable() to replace atomic mapping.

[1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com
[2]: https://patchwork.freedesktop.org/patch/295840/

Suggested-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
---
Suggested by credits:
  Ira: Referred to his suggestions about keeping pagefault_disable().
---
 drivers/gpu/drm/i915/gem/i915_gem_shmem.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
index f42ca1179f37..e279a3e30c02 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
@@ -472,11 +472,13 @@ shmem_pwrite(struct drm_i915_gem_object *obj,
 		if (err < 0)
 			return err;
 
-		vaddr = kmap_atomic(page);
+		vaddr = kmap_local_page(page);
+		pagefault_disable();
 		unwritten = __copy_from_user_inatomic(vaddr + pg,
 						      user_data,
 						      len);
-		kunmap_atomic(vaddr);
+		pagefault_enable();
+		kunmap_local(vaddr);
 
 		err = aops->write_end(obj->base.filp, mapping, offset, len,
 				      len - unwritten, page, data);
-- 
2.34.1