linux-kernel - Re: [PATCH] drm/amd/amdgpu: Replace kmap() with kmap_local

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] [day] [month] [year] [list]

Message-ID: <ebb573b8-237f-602e-8d7d-9c49f0bd73be@gmail.com>
Date:   Sun, 14 Aug 2022 19:14:31 +0200
From:   Christian König <ckoenig.leichtzumerken@...il.com>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Nirmoy Das <nirmoy.das@....com>,
        Jonathan Kim <jonathan.kim@....com>,
        Philip Yang <Philip.Yang@....com>,
        Matthew Auld <matthew.auld@...el.com>,
        Zack Rusin <zackr@...are.com>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org
Cc:     Ira Weiny <ira.weiny@...el.com>
Subject: Re: [PATCH] drm/amd/amdgpu: Replace kmap() with kmap_local_page()

Am 12.08.22 um 19:57 schrieb Fabio M. De Francesco:
> kmap() is being deprecated in favor of kmap_local_page().
>
> There are two main problems with kmap(): (1) It comes with an overhead as
> 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 are still valid.
>
> Since its use in amdgpu/amdgpu_ttm.c is safe, it should be preferred.
>
> Therefore, replace kmap() with kmap_local_page() in amdgpu/amdgpu_ttm.c.
>
> Suggested-by: Ira Weiny <ira.weiny@...el.com>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>

For those two use cases that looks good to me. Feel free to add an 
Acked-by: Christian König <christian.koenig@....com>

Regards,
Christian.

> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index 3b4c19412625..c11657b5915f 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -2301,9 +2301,9 @@ static ssize_t amdgpu_iomem_read(struct file *f, char __user *buf,
>   		if (p->mapping != adev->mman.bdev.dev_mapping)
>   			return -EPERM;
>   
> -		ptr = kmap(p);
> +		ptr = kmap_local_page(p);
>   		r = copy_to_user(buf, ptr + off, bytes);
> -		kunmap(p);
> +		kunmap_local(ptr);
>   		if (r)
>   			return -EFAULT;
>   
> @@ -2352,9 +2352,9 @@ static ssize_t amdgpu_iomem_write(struct file *f, const char __user *buf,
>   		if (p->mapping != adev->mman.bdev.dev_mapping)
>   			return -EPERM;
>   
> -		ptr = kmap(p);
> +		ptr = kmap_local_page(p);
>   		r = copy_from_user(ptr + off, buf, bytes);
> -		kunmap(p);
> +		kunmap_local(ptr);
>   		if (r)
>   			return -EFAULT;
>