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Tue, 30 Sep 2025 12:30:08 +0200 (CEST) Date: Tue, 30 Sep 2025 12:30:03 +0200 From: Boris Brezillon To: =?UTF-8?B?TG/Dr2M=?= Molinari Cc: Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , Rob Herring , Steven Price , Liviu Dudau , Melissa Wen , =?UTF-8?B?TWHDrXJh?= Canal , Hugh Dickins , Baolin Wang , Andrew Morton , Al Viro , =?UTF-8?B?TWlrb8WCYWo=?= Wasiak , Christian Brauner , Nitin Gote , Andi Shyti , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, linux-mm@kvack.org, kernel@collabora.com Subject: Re: [PATCH 2/8] drm/gem: Introduce drm_gem_get_unmapped_area() fop Message-ID: <20250930123003.75370854@fedora> In-Reply-To: <20250929200316.18417-3-loic.molinari@collabora.com> References: <20250929200316.18417-1-loic.molinari@collabora.com> <20250929200316.18417-3-loic.molinari@collabora.com> Organization: Collabora X-Mailer: Claws Mail 4.3.1 (GTK 3.24.49; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: D9D7B160013 X-Stat-Signature: ne4yp7gdcegbyndnns131yneigcht367 X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1759228211-52554 X-HE-Meta: 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 Jw4e8Ymm Fl7HK5ry9hqYKgAQa2ZWAmScht4RFjJPN86C9DwwI09LxT6j6b7mO7YnxyetENTVyyFzv4GgXswkm6H+JSPU9MFMKc8oBzpCcx9oDgSGnsp7hNJFO5PtEBl8EMqJXKg6FzZnUzZdaaYfwF7B20k86VEabdIvaOyeKNJ4lso2SekWH1LmdU6DhRjFymClu6TnkfGK357B/O6ffaDbiAySy/EsBSyIRZ7cEGs5AAsB9SNPWtH+Id5IU8oWNj7hywj6F3T52v1Kj1fQDvtEBibZKBiOh/rdw1chEA6wZbn/vcJtk5+g8treX5EiFbCGkVLB9lS1w3V7O5rcWWhTdcWEiYpqioSqDGvy9KxusLr7u3oJ9Qhcpinigeq6KQ1dHgbO0kH8UI7S+ACj3imrK047DZHvvb4B3VH0xs+DLZcGnqkIdh+WwMHRvdcFEs+ywRC1z63+i X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 29 Sep 2025 22:03:10 +0200 Lo=C3=AFc Molinari wrote: > mmap() calls on the drm file pointer currently always end up using > mm_get_unmapped_area() to get a free mapping region. On builds with > CONFIG_TRANSPARENT_HUGEPAGE enabled, this isn't ideal for GEM objects > backed by shmem buffers on mount points setting the 'huge=3D' option > because it can't correctly figure out the potentially huge address > alignment required. >=20 > This commit introduces the drm_gem_get_unmapped_area() function which > is meant to be used as a get_unmapped_area file operation on the drm > file pointer to lookup GEM objects based on their fake offsets and get > a properly aligned region by calling shmem_get_unmapped_area() with > the right file pointer. If a GEM object isn't available at the given > offset or if the caller isn't granted access to it, the function falls > back to mm_get_unmapped_area(). >=20 > This also makes drm_gem_get_unmapped_area() part of the default GEM > file operations so that all the drm drivers can benefit from more > efficient mappings thanks to the huge page fault handler introduced in > previous commit 'drm/shmem-helper: Add huge page fault handler'. >=20 > The shmem_get_unmapped_area() function needs to be exported so that > it can be used from the drm subsystem. >=20 > Signed-off-by: Lo=C3=AFc Molinari > --- > drivers/gpu/drm/drm_gem.c | 110 ++++++++++++++++++++++++++++++-------- > include/drm/drm_gem.h | 4 ++ > mm/shmem.c | 1 + > 3 files changed, 93 insertions(+), 22 deletions(-) >=20 > diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c > index cbeb76b2124f..d027db462c2d 100644 > --- a/drivers/gpu/drm/drm_gem.c > +++ b/drivers/gpu/drm/drm_gem.c > @@ -1187,36 +1187,27 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj, = unsigned long obj_size, > } > EXPORT_SYMBOL(drm_gem_mmap_obj); > =20 > -/** > - * drm_gem_mmap - memory map routine for GEM objects > - * @filp: DRM file pointer > - * @vma: VMA for the area to be mapped > - * > - * If a driver supports GEM object mapping, mmap calls on the DRM file > - * descriptor will end up here. > - * > - * Look up the GEM object based on the offset passed in (vma->vm_pgoff w= ill > - * contain the fake offset we created when the GTT map ioctl was called = on > - * the object) and map it with a call to drm_gem_mmap_obj(). > - * > - * If the caller is not granted access to the buffer object, the mmap wi= ll fail > - * with EACCES. Please see the vma manager for more information. > +/* > + * Look up a GEM object in offset space based on the exact start address= . The > + * caller must be granted access to the object. Returns a GEM object on = success > + * or a negative error code on failure. The returned GEM object needs to= be > + * released with drm_gem_object_put(). > */ > -int drm_gem_mmap(struct file *filp, struct vm_area_struct *vma) > +static struct drm_gem_object * > +drm_gem_object_lookup_from_offset(struct file *filp, unsigned long start, > + unsigned long pages) > { > struct drm_file *priv =3D filp->private_data; > struct drm_device *dev =3D priv->minor->dev; > struct drm_gem_object *obj =3D NULL; > struct drm_vma_offset_node *node; > - int ret; > =20 > if (drm_dev_is_unplugged(dev)) > - return -ENODEV; > + return ERR_PTR(-ENODEV); > =20 > drm_vma_offset_lock_lookup(dev->vma_offset_manager); > node =3D drm_vma_offset_exact_lookup_locked(dev->vma_offset_manager, > - vma->vm_pgoff, > - vma_pages(vma)); > + start, pages); > if (likely(node)) { > obj =3D container_of(node, struct drm_gem_object, vma_node); > /* > @@ -1235,14 +1226,89 @@ int drm_gem_mmap(struct file *filp, struct vm_are= a_struct *vma) > drm_vma_offset_unlock_lookup(dev->vma_offset_manager); > =20 > if (!obj) > - return -EINVAL; > + return ERR_PTR(-EINVAL); > =20 > if (!drm_vma_node_is_allowed(node, priv)) { > drm_gem_object_put(obj); > - return -EACCES; > + return ERR_PTR(-EACCES); > } > =20 > - ret =3D drm_gem_mmap_obj(obj, drm_vma_node_size(node) << PAGE_SHIFT, > + return obj; > +} > + > +/** > + * drm_gem_get_unmapped_area - get memory mapping region routine for GEM= objects > + * @filp: DRM file pointer > + * @uaddr: User address hint > + * @len: Mapping length > + * @pgoff: Offset (in pages) > + * @flags: Mapping flags > + * > + * If a driver supports GEM object mapping, before ending up in drm_gem_= mmap(), > + * mmap calls on the DRM file descriptor will first try to find a free l= inear > + * address space large enough for a mapping. Since GEM objects are backe= d by > + * shmem buffers, this should preferably be handled by the shmem virtual= memory > + * filesystem which can appropriately align addresses to huge page sizes= when > + * needed. > + * > + * Look up the GEM object based on the offset passed in (vma->vm_pgoff w= ill > + * contain the fake offset we created) and call shmem_get_unmapped_area(= ) with > + * the right file pointer. > + * > + * If a GEM object is not available at the given offset or if the caller= is not > + * granted access to it, fall back to mm_get_unmapped_area(). > + */ > +unsigned long drm_gem_get_unmapped_area(struct file *filp, unsigned long= uaddr, > + unsigned long len, unsigned long pgoff, > + unsigned long flags) > +{ > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE > + struct drm_gem_object *obj; > + unsigned long ret; > + > + obj =3D drm_gem_object_lookup_from_offset(filp, pgoff, len >> PAGE_SHIF= T); > + if (IS_ERR(obj)) Is this supposed to happen? If not, I'd be tempted to add a WARN_ON_ONCE(). > + return mm_get_unmapped_area(current->mm, filp, uaddr, len, 0, > + flags); > + > + ret =3D shmem_get_unmapped_area(obj->filp, uaddr, len, 0, flags); > + > + drm_gem_object_put(obj); > + > + return ret; > +#else > + return mm_get_unmapped_area(current->mm, filp, uaddr, len, 0, flags); Looks like the above code covers the non-THP case too, do we really need to specialize for !CONFIG_TRANSPARENT_HUGEPAGE here? > +#endif > +} > +EXPORT_SYMBOL(drm_gem_get_unmapped_area); > + > +/** > + * drm_gem_mmap - memory map routine for GEM objects > + * @filp: DRM file pointer > + * @vma: VMA for the area to be mapped > + * > + * If a driver supports GEM object mapping, mmap calls on the DRM file > + * descriptor will end up here. > + * > + * Look up the GEM object based on the offset passed in (vma->vm_pgoff w= ill > + * contain the fake offset we created) and map it with a call to > + * drm_gem_mmap_obj(). > + * > + * If the caller is not granted access to the buffer object, the mmap wi= ll fail > + * with EACCES. Please see the vma manager for more information. > + */ > +int drm_gem_mmap(struct file *filp, struct vm_area_struct *vma) > +{ > + struct drm_gem_object *obj; > + int ret; > + > + obj =3D drm_gem_object_lookup_from_offset(filp, vma->vm_pgoff, > + vma_pages(vma)); > + if (IS_ERR(obj)) > + return PTR_ERR(obj); > + > + ret =3D drm_gem_mmap_obj(obj, > + drm_vma_node_size(&obj->vma_node) << PAGE_SHIFT, > vma); > =20 > drm_gem_object_put(obj); > diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h > index 8d48d2af2649..7c8bd67d087c 100644 > --- a/include/drm/drm_gem.h > +++ b/include/drm/drm_gem.h > @@ -469,6 +469,7 @@ struct drm_gem_object { > .poll =3D drm_poll,\ > .read =3D drm_read,\ > .llseek =3D noop_llseek,\ > + .get_unmapped_area =3D drm_gem_get_unmapped_area,\ > .mmap =3D drm_gem_mmap, \ > .fop_flags =3D FOP_UNSIGNED_OFFSET > =20 > @@ -506,6 +507,9 @@ void drm_gem_vm_close(struct vm_area_struct *vma); > int drm_gem_mmap_obj(struct drm_gem_object *obj, unsigned long obj_size, > struct vm_area_struct *vma); > int drm_gem_mmap(struct file *filp, struct vm_area_struct *vma); > +unsigned long drm_gem_get_unmapped_area(struct file *filp, unsigned long= uaddr, > + unsigned long len, unsigned long pgoff, > + unsigned long flags); > =20 > /** > * drm_gem_object_get - acquire a GEM buffer object reference > diff --git a/mm/shmem.c b/mm/shmem.c > index e2c76a30802b..b2f41b430daa 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -2915,6 +2915,7 @@ unsigned long shmem_get_unmapped_area(struct file *= file, > return addr; > return inflated_addr; > } > +EXPORT_SYMBOL_GPL(shmem_get_unmapped_area); > =20 > #ifdef CONFIG_NUMA > static int shmem_set_policy(struct vm_area_struct *vma, struct mempolicy= *mpol)