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Date:   Thu, 13 Oct 2022 19:41:39 -0700
From:   Kees Cook <>
To:     "Fabio M. De Francesco" <>
Cc:     Alex Deucher <>,
        Christian König <>,
        "Pan, Xinhui" <>,
        David Airlie <>,
        Daniel Vetter <>,
        Christian Brauner <>,
        Sumit Semwal <>,
        Jean Delvare <>,
        Guenter Roeck <>,,,,,,,,,
        "Venkataramanan, Anirudh" <>,
        Ira Weiny <>
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" <>
> Suggested-by: Ira Weiny <>
> Signed-off-by: Fabio M. De Francesco <>

Reviewed-by: Kees Cook <>

Kees Cook

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