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Date: Mon, 17 Oct 2022 12:52:10 -0400 From: Alex Deucher <alexdeucher@...il.com> To: Christian König <christian.koenig@....com> Cc: "Fabio M. De Francesco" <fmdefrancesco@...il.com>, Alex Deucher <alexander.deucher@....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>, Kees Cook <keescook@...omium.org>, 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() Applied. Thanks! On Fri, Oct 14, 2022 at 3:03 AM Christian König <christian.koenig@....com> wrote: > > Am 13.10.22 um 23:07 schrieb Fabio M. De Francesco: > > 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: Christian König <christian.koenig@....com> > > > --- > > drivers/gpu/drm/radeon/radeon_ttm.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/gpu/drm/radeon/radeon_ttm.c b/drivers/gpu/drm/radeon/radeon_ttm.c > > index d33fec488713..bdb4c0e0736b 100644 > > --- a/drivers/gpu/drm/radeon/radeon_ttm.c > > +++ b/drivers/gpu/drm/radeon/radeon_ttm.c > > @@ -869,11 +869,11 @@ static ssize_t radeon_ttm_gtt_read(struct file *f, char __user *buf, > > > > page = rdev->gart.pages[p]; > > if (page) { > > - ptr = kmap(page); > > + ptr = kmap_local_page(page); > > ptr += off; > > > > r = copy_to_user(buf, ptr, cur_size); > > - kunmap(rdev->gart.pages[p]); > > + kunmap_local(ptr); > > } else > > r = clear_user(buf, cur_size); > > >
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