linux-kernel - Re: [PATCH] drm/i915: Call page_address() on page acquired with GFP

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Message-ID: <bebd57fc-7135-dc97-701e-54cb9c2955c0@linux.intel.com>
Date:   Wed, 14 Jun 2023 14:22:23 +0100
From:   Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
To:     Sumitra Sharma <sumitraartsy@...il.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Cc:     Ira Weiny <ira.weiny@...el.com>, Fabio <fmdefrancesco@...il.com>,
        Deepak R Varma <drv@...lo.com>,
        Thomas Hellstrom <thomas.hellstrom@...el.com>,
        Matthew Auld <matthew.auld@...el.com>
Subject: Re: [PATCH] drm/i915: Call page_address() on page acquired with
 GFP_KERNEL flag


On 14/06/2023 13:35, Sumitra Sharma wrote:
> Pages allocated with GFP_KERNEL cannot come from Highmem.
> That is why there is no need to call kmap() on them.

Are you sure it is GFP_KERNEL backed and not tmpfs? I am not sure myself 
so let me copy Matt and Thomas if they happen to know off hand.

Regards,

Tvrtko

> Therefore, don't call kmap() on the page coming from
> vma_res->bi.pages using for_each_sgt_page() in
> i915_vma_coredump_create().
> 
> Use a plain page_address() to get the kernel address instead.
> 
> Signed-off-by: Sumitra Sharma <sumitraartsy@...il.com>
> ---
>   drivers/gpu/drm/i915/i915_gpu_error.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
> index f020c0086fbc..6f51cb4fc55c 100644
> --- a/drivers/gpu/drm/i915/i915_gpu_error.c
> +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
> @@ -1164,9 +1164,8 @@ i915_vma_coredump_create(const struct intel_gt *gt,
>   
>   			drm_clflush_pages(&page, 1);
>   
> -			s = kmap(page);
> +			s = page_address(page);
>   			ret = compress_page(compress, s, dst, false);
> -			kunmap(page);
>   
>   			drm_clflush_pages(&page, 1);
>