linux-kernel - [PATCH v3 3/9] drm/i915: Use kmap_local_page() in gem/i915_gem

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20231203132947.2328805-4-zhao1.liu@linux.intel.com>
Date:   Sun,  3 Dec 2023 21:29:41 +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>,
        Ira Weiny <ira.weiny@...el.com>,
        "Fabio M . De Francesco" <fmdefrancesco@...il.com>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Zhenyu Wang <zhenyu.z.wang@...el.com>,
        Zhao Liu <zhao1.liu@...el.com>
Subject: [PATCH v3 3/9] drm/i915: Use kmap_local_page() in gem/i915_gem_shmem.c

From: Zhao Liu <zhao1.liu@...el.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 (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 or preemption disables.

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@...el.com>
Suggested-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
Signed-off-by: Zhao Liu <zhao1.liu@...el.com>
Reviewed-by: Ira Weiny <ira.weiny@...el.com>
Reviewed-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
---
Suggested by credits:
  Ira: Referred to his suggestions about keeping pagefault_disable().
  Fabio: Referred to his description about why kmap_local_page() should
         be preferred.
---
 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 73a4a4eb29e0..38b72d86560f 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
@@ -485,11 +485,13 @@ 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