From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bali.collaboradmins.com (bali.collaboradmins.com [148.251.105.195]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 752482F9DAA for ; Tue, 30 Sep 2025 10:30:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.251.105.195 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759228214; cv=none; b=aBIqna9Zk+9j9Kyf2TwYPYM2nmfaMdhk3JHqJ6CpP9KgCUrEfT2MxsIvMfz0Dv1eixodWxJL1J3IgMiJZgQQU/aVsMqQimSJ7VUNEQEbv/HnrIpVqafkAZSa5z6mEYnSpOjHYMC8mohWybZrkOPw1WQ7dCERnXy5hiUV+cRc1q8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759228214; c=relaxed/simple; bh=3mTTpLiMqnXjtsubYnc/0h302ORdA8DbizXcRRMB8YI=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=Vvo7RDV/swda5o5N3FAPHmj+vlvPpFpjJAq0JuK/rItfmLe/sce2U7e/ISB4p8Pn5sWLWkbDEgIxoUK2PaYFOSiY5ahJFqZWePDxXhEMIn//bgl1UPhT4VApCTJ5B9tD2jGdFFG1B/2isz+hv0rfRjRKNdmTLl1fz2rUAKP6Tjg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com; spf=pass smtp.mailfrom=collabora.com; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b=jKq8joig; arc=none smtp.client-ip=148.251.105.195 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=collabora.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b="jKq8joig" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1759228209; bh=3mTTpLiMqnXjtsubYnc/0h302ORdA8DbizXcRRMB8YI=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=jKq8joigCrtAG9Qt4gVEr7ETSzSYaNE4I9ApnBM8V78qDeF0YbigN7S+RDAn9Cy87 cv5VFUuOpqSgaIAoDAme8WyKJUGzxlGjprctBQJhHeLX2OhvZeLUvMH2hvQ/lFP/iI uQOs+MuLqvLRosA1DccwsBNHw8zJlfTnlNbb450S193Wg29c7JlkX5KNhaxALfqRWU oZuysLeigN5GUoOIT45tWV973qEUR+AXE4Zu5z9XYUFWFVOmt4GSlH91mKDWYBKesn eKZQjq7Z3dso39uQuZmuaUPL/Gv6ONeNDxhHdxPuxKscgOANt6/R2hnbgaErI6/8N+ yAdWjZppvgFyQ== Received: from fedora (unknown [IPv6:2a01:e0a:2c:6930:d919:a6e:5ea1:8a9f]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: bbrezillon) by bali.collaboradmins.com (Postfix) with ESMTPSA id 65F6617E0097; 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) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable 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)