linux-kernel - Re: [PATCH 1/7] drm/i915: Replace kmap() with kmap_local

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Date:   Mon, 13 Dec 2021 14:39:59 +0200
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     ira.weiny@...el.com
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Patrik Jakobsson <patrik.r.jakobsson@...il.com>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        linux-arm-msm@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        amd-gfx@...ts.freedesktop.org
Subject: Re: [PATCH 1/7] drm/i915: Replace kmap() with kmap_local_page()

On Fri, Dec 10, 2021 at 03:23:58PM -0800, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> kmap() is being deprecated and these usages are all local to the thread
> so there is no reason kmap_local_page() can't be used.
> 
> Replace kmap() calls with kmap_local_page().
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_shmem.c          | 4 ++--
>  drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c | 8 ++++----
>  drivers/gpu/drm/i915/gt/intel_ggtt_fencing.c       | 4 ++--
>  drivers/gpu/drm/i915/gt/shmem_utils.c              | 4 ++--
>  drivers/gpu/drm/i915/i915_gem.c                    | 8 ++++----
>  drivers/gpu/drm/i915/i915_gpu_error.c              | 4 ++--
>  6 files changed, 16 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
> index d77da59fae04..fa8b820e14aa 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
> @@ -597,9 +597,9 @@ i915_gem_object_create_shmem_from_data(struct drm_i915_private *dev_priv,
>  		if (err < 0)
>  			goto fail;
>  
> -		vaddr = kmap(page);
> +		vaddr = kmap_local_page(page);
>  		memcpy(vaddr, data, len);
> -		kunmap(page);
> +		kunmap_local(vaddr);
>  
>  		err = pagecache_write_end(file, file->f_mapping,
>  					  offset, len, len,
> diff --git a/drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c
> index 6d30cdfa80f3..e59e1725e29d 100644
> --- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c
> +++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c
> @@ -144,7 +144,7 @@ static int check_partial_mapping(struct drm_i915_gem_object *obj,
>  	intel_gt_flush_ggtt_writes(&to_i915(obj->base.dev)->gt);
>  
>  	p = i915_gem_object_get_page(obj, offset >> PAGE_SHIFT);
> -	cpu = kmap(p) + offset_in_page(offset);
> +	cpu = kmap_local_page(p) + offset_in_page(offset);

Does kunmap_local() do some magic to make it work even when you
don't pass in the same value you got from kmap_local_page()?

>  	drm_clflush_virt_range(cpu, sizeof(*cpu));
>  	if (*cpu != (u32)page) {
>  		pr_err("Partial view for %lu [%u] (offset=%llu, size=%u [%llu, row size %u], fence=%d, tiling=%d, stride=%d) misalignment, expected write to page (%llu + %u [0x%llx]) of 0x%x, found 0x%x\n",
> @@ -162,7 +162,7 @@ static int check_partial_mapping(struct drm_i915_gem_object *obj,
>  	}
>  	*cpu = 0;
>  	drm_clflush_virt_range(cpu, sizeof(*cpu));
> -	kunmap(p);
> +	kunmap_local(cpu);
>  
>  out:
>  	__i915_vma_put(vma);

-- 
Ville Syrjälä
Intel