linux-kernel - Re: [PATCH 5/9] drm/panfrost: Handle page mapping failure

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Message-ID: <20241021163227.1312bbcd@collabora.com>
Date: Mon, 21 Oct 2024 16:32:27 +0200
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Adrián Larumbe <adrian.larumbe@...labora.com>
Cc: Rob Herring <robh@...nel.org>, Steven Price <steven.price@....com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
 <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David Airlie
 <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Philipp Zabel
 <p.zabel@...gutronix.de>, kernel@...labora.com,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/9] drm/panfrost: Handle page mapping failure

On Tue, 15 Oct 2024 00:31:40 +0100
Adrián Larumbe <adrian.larumbe@...labora.com> wrote:

> -			ops->map_pages(ops, iova, paddr, pgsize, pgcount, prot,
> +			ret = ops->map_pages(ops, iova, paddr, pgsize, pgcount, prot,
>  				       GFP_KERNEL, &mapped);
> +			if (ret) {
> +				/* Unmap everything we mapped and bail out */
> +				mmu_unmap_range(mapped, start_iova, is_heap, ops);
> +				return ret;
> +			}

I'm pretty sure you don't need to know whether this is a heap BO or not
in that path. All you need to do is unmap what you've already mapped,
which gives you some guarantees:

- the pages you unmap must be present (no need to iova_to_phys())
- unmapping one 2M page at a time is not needed, because you know where
  the mapped region starts/ends, so you don't need this
  "is-this-the-end-of-the-heap-buffer" check that forces us to scan 2M
  at a time