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Date:   Fri, 7 Jul 2023 13:00:10 +0200
From:   Boris Brezillon <boris.brezillon@collabora.com>
To:     Danilo Krummrich <dakr@redhat.com>
Cc:     airlied@gmail.com, daniel@ffwll.ch, tzimmermann@suse.de,
        mripard@kernel.org, corbet@lwn.net, christian.koenig@amd.com,
        bskeggs@redhat.com, Liam.Howlett@oracle.com,
        matthew.brost@intel.com, alexdeucher@gmail.com, ogabbay@kernel.org,
        bagasdotme@gmail.com, willy@infradead.org, jason@jlekstrand.net,
        dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        Donald Robson <donald.robson@imgtec.com>,
        Dave Airlie <airlied@redhat.com>
Subject: Re: [PATCH drm-next v6 02/13] drm: manager to keep track of GPUs VA
 mappings
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In-Reply-To: <20230629222651.3196-3-dakr@redhat.com>
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        <20230629222651.3196-3-dakr@redhat.com>
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On Fri, 30 Jun 2023 00:25:18 +0200
Danilo Krummrich <dakr@redhat.com> wrote:

> +/**
> + * drm_gpuva_for_each_va_range - iternator to walk over a range of &drm_gpuvas
> + * @va__: &drm_gpuva structure to assign to in each iteration step
> + * @mgr__: &drm_gpuva_manager to walk over
> + * @start__: starting offset, the first gpuva will overlap this
> + * @end__: ending offset, the last gpuva will start before this (but may
> + * overlap)
> + *
> + * This iterator walks over all &drm_gpuvas in the &drm_gpuva_manager that lie
> + * between @start__ and @end__. It is implemented similarly to list_for_each(),
> + * but is using the &drm_gpuva_manager's internal interval tree to accelerate
> + * the search for the starting &drm_gpuva, and hence isn't safe against removal
> + * of elements. It assumes that @end__ is within (or is the upper limit of) the
> + * &drm_gpuva_manager. This iterator does not skip over the &drm_gpuva_manager's
> + * @kernel_alloc_node.
> + */
> +#define drm_gpuva_for_each_va_range(va__, mgr__, start__, end__) \
> +	for (va__ = drm_gpuva_find_first((mgr__), (start__), (end__)); \

drm_gpuva_find_first() takes the range size as its last argument, not
the range end:

	for (va__ = drm_gpuva_find_first((mgr__), (start__), (end__) - (start__)); \


> +	     va__ && (va__->va.addr < (end__)) && \
> +	     !list_entry_is_head(va__, &(mgr__)->rb.list, rb.entry); \
> +	     va__ = list_next_entry(va__, rb.entry))

If you define:

static inline struct drm_gpuva *
drm_gpuva_next(struct drm_gpuva *va)
{
	if (va && !list_is_last(&va->rb.entry, &va->mgr->rb.list))
		return list_next_entry(va, rb.entry);

	return NULL;
}

the for loop becomes a bit more readable:

	for (va__ = drm_gpuva_find_first((mgr__), (start__), (end__) - (start__)); \
	     va__ && (va__->va.addr < (end__)); \
	     va__ = drm_gpuva_next(va__))

> +
> +/**
> + * drm_gpuva_for_each_va_range_safe - iternator to safely walk over a range of
> + * &drm_gpuvas
> + * @va__: &drm_gpuva to assign to in each iteration step
> + * @next__: another &drm_gpuva to use as temporary storage
> + * @mgr__: &drm_gpuva_manager to walk over
> + * @start__: starting offset, the first gpuva will overlap this
> + * @end__: ending offset, the last gpuva will start before this (but may
> + * overlap)
> + *
> + * This iterator walks over all &drm_gpuvas in the &drm_gpuva_manager that lie
> + * between @start__ and @end__. It is implemented similarly to
> + * list_for_each_safe(), but is using the &drm_gpuva_manager's internal interval
> + * tree to accelerate the search for the starting &drm_gpuva, and hence is safe
> + * against removal of elements. It assumes that @end__ is within (or is the
> + * upper limit of) the &drm_gpuva_manager. This iterator does not skip over the
> + * &drm_gpuva_manager's @kernel_alloc_node.
> + */
> +#define drm_gpuva_for_each_va_range_safe(va__, next__, mgr__, start__, end__) \
> +	for (va__ = drm_gpuva_find_first((mgr__), (start__), (end__)), \
> +	     next__ = va ? list_next_entry(va__, rb.entry) : NULL; \
> +	     va__ && (va__->va.addr < (end__)) && \
> +	     !list_entry_is_head(va__, &(mgr__)->rb.list, rb.entry); \
> +	     va__ = next__, next__ = list_next_entry(va__, rb.entry))

And this is the safe version using the drm_gpuva_next() helper:

	for (va__ = drm_gpuva_find_first((mgr__), (start__), (end__) - (start__)), \
	     next__ = drm_gpuva_next(va__); \
	     va__ && (va__->va.addr < (end__)); \
	     va__ = next__, next__ = drm_gpuva_next(va__))

Those changes fixed an invalid pointer access I had in the sm_unmap()
path.