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Date: Thu, 13 Oct 2022 19:41:39 -0700 From: Kees Cook <keescook@...omium.org> To: "Fabio M. De Francesco" <fmdefrancesco@...il.com> Cc: Alex Deucher <alexander.deucher@....com>, Christian König <christian.koenig@....com>, "Pan, Xinhui" <Xinhui.Pan@....com>, David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, Christian Brauner <brauner@...nel.org>, Sumit Semwal <sumit.semwal@...aro.org>, Jean Delvare <jdelvare@...e.com>, Guenter Roeck <linux@...ck-us.net>, amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, bpf@...r.kernel.org, linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org, linux-hwmon@...r.kernel.org, linux-hardening@...r.kernel.org, "Venkataramanan, Anirudh" <anirudh.venkataramanan@...el.com>, Ira Weiny <ira.weiny@...el.com> Subject: Re: [PATCH] drm/radeon: Replace kmap() with kmap_local_page() On Thu, Oct 13, 2022 at 11:07:14PM +0200, Fabio M. De Francesco wrote: > The use of kmap() is being deprecated in favor of kmap_local_page(). > > There are two main problems with kmap(): (1) It comes with an overhead as > the mapping space is restricted and protected by a global lock for > synchronization and (2) it also requires global TLB invalidation when the > kmap’s pool wraps and it might block when the mapping space is fully > utilized until a slot becomes available. > > With kmap_local_page() the mappings are per thread, CPU local, can take > page faults, and can be called from any context (including interrupts). > It is faster than kmap() in kernels with HIGHMEM enabled. Furthermore, > the tasks can be preempted and, when they are scheduled to run again, the > kernel virtual addresses are restored and still valid. > > Therefore, replace kmap() with kmap_local_page() in radeon_ttm_gtt_read(). > > Cc: "Venkataramanan, Anirudh" <anirudh.venkataramanan@...el.com> > Suggested-by: Ira Weiny <ira.weiny@...el.com> > Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com> Reviewed-by: Kees Cook <keescook@...omium.org> -- Kees Cook
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