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Mon, 1 Dec 2025 09:33:08 +0100 (CET) Date: Mon, 1 Dec 2025 09:33:04 +0100 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 , Jonathan Corbet , Christopher Healy , Matthew Wilcox , Bagas Sanjaya , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, linux-mm@kvack.org, linux-doc@vger.kernel.org, kernel@collabora.com Subject: Re: [PATCH v10 03/10] drm/gem: Introduce drm_gem_get_unmapped_area() fop Message-ID: <20251201093304.285e929f@fedora> In-Reply-To: <20251128185252.3092-4-loic.molinari@collabora.com> References: <20251128185252.3092-1-loic.molinari@collabora.com> <20251128185252.3092-4-loic.molinari@collabora.com> Organization: Collabora X-Mailer: Claws Mail 4.3.1 (GTK 3.24.51; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Stat-Signature: 7jurhbwrcewxa1ys8dam31gwhd39pgso X-Rspam-User: X-Rspamd-Queue-Id: 19C612000B X-Rspamd-Server: rspam09 X-HE-Tag: 1764577991-433459 X-HE-Meta: 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 cNW9gYxB gPdIt 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 Fri, 28 Nov 2025 19:52:45 +0100 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 mountpoints 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 > v3: > - include in drm_gem.c > - forward to shmem layer in builds with CONFIG_TRANSPARENT_HUGEPAGE=3Dn >=20 > v6: > - use GPL variant to export drm_gem_get_unmapped_area() > - don't export shmem_get_unmapped_area() anymore (use f_op instead) >=20 > Signed-off-by: Lo=C3=AFc Molinari Reviewed-by: Boris Brezillon Renaming suggestion below (feel free to ignore). > --- > drivers/gpu/drm/drm_gem.c | 108 ++++++++++++++++++++++++++++++-------- > include/drm/drm_gem.h | 4 ++ > 2 files changed, 90 insertions(+), 22 deletions(-) >=20 > diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c > index efc79bbf3c73..41d344c270a7 100644 > --- a/drivers/gpu/drm/drm_gem.c > +++ b/drivers/gpu/drm/drm_gem.c > @@ -36,6 +36,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -1177,36 +1178,27 @@ 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) nit: I'd name that one drm_gem_object_at_offset(). > { > 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); > /* > @@ -1225,14 +1217,86 @@ 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) > +{ > + 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) || !obj->filp || !obj->filp->f_op->get_unmapped_area) > + return mm_get_unmapped_area(current->mm, filp, uaddr, len, 0, > + flags); > + > + ret =3D obj->filp->f_op->get_unmapped_area(obj->filp, uaddr, len, 0, > + flags); > + > + drm_gem_object_put(obj); > + > + return ret; > +} > +EXPORT_SYMBOL_GPL(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