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(unknown [IPv6:2a01:e0a:5e3:6100:826d:bc07:e98c:84a]) (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: loicmolinari) by bali.collaboradmins.com (Postfix) with ESMTPSA id BB76A17E1404; Tue, 21 Oct 2025 13:30:56 +0200 (CEST) From: =?UTF-8?q?Lo=C3=AFc=20Molinari?= To: Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , Boris Brezillon , Rob Herring , Steven Price , Liviu Dudau , Melissa Wen , =?UTF-8?q?Ma=C3=ADra=20Canal?= , Hugh Dickins , Baolin Wang , Andrew Morton , =?UTF-8?q?Lo=C3=AFc=20Molinari?= , Al Viro , =?UTF-8?q?Miko=C5=82aj=20Wasiak?= , Christian Brauner , Nitin Gote , Andi Shyti , Jonathan Corbet , Christopher Healy , Matthew Wilcox , Bagas Sanjaya Cc: 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: [PATCH v5 02/12] drm/shmem-helper: Implement map_pages fault-around handler Date: Tue, 21 Oct 2025 13:30:39 +0200 Message-ID: <20251021113049.17242-3-loic.molinari@collabora.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20251021113049.17242-1-loic.molinari@collabora.com> References: <20251021113049.17242-1-loic.molinari@collabora.com> 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 This gives the mm subsystem the ability to increase fault handling performance by proposing the insertion of a range of pages around the faulty address in a single batch. v4: - implement map_pages instead of huge_fault v5: - improve patch series progression - use dma_resv_trylock() in map_pages (many thanks to Matthew Wilcox) - validate map_pages range based on end_pgoff instead of start_pgoff Signed-off-by: Lo=C3=AFc Molinari --- drivers/gpu/drm/drm_gem_shmem_helper.c | 72 ++++++++++++++++++++++---- 1 file changed, 62 insertions(+), 10 deletions(-) diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_g= em_shmem_helper.c index be89be1c804c..2a9fbc9c3712 100644 --- a/drivers/gpu/drm/drm_gem_shmem_helper.c +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c @@ -567,31 +567,82 @@ int drm_gem_shmem_dumb_create(struct drm_file *file, = struct drm_device *dev, } EXPORT_SYMBOL_GPL(drm_gem_shmem_dumb_create); =20 -static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf) +static bool drm_gem_shmem_fault_is_valid(struct drm_gem_object *obj, + pgoff_t pgoff) +{ + struct drm_gem_shmem_object *shmem =3D to_drm_gem_shmem_obj(obj); + + if (drm_WARN_ON_ONCE(obj->dev, !shmem->pages) || + pgoff >=3D (obj->size >> PAGE_SHIFT) || + shmem->madv < 0) + return false; + + return true; +} + +static vm_fault_t drm_gem_shmem_map_pages(struct vm_fault *vmf, + pgoff_t start_pgoff, + pgoff_t end_pgoff) { struct vm_area_struct *vma =3D vmf->vma; struct drm_gem_object *obj =3D vma->vm_private_data; struct drm_gem_shmem_object *shmem =3D to_drm_gem_shmem_obj(obj); - loff_t num_pages =3D obj->size >> PAGE_SHIFT; + struct page **pages =3D shmem->pages; + unsigned long addr, pfn; vm_fault_t ret; - struct page *page; + + start_pgoff -=3D vma->vm_pgoff; + end_pgoff -=3D vma->vm_pgoff; + addr =3D vma->vm_start + (start_pgoff << PAGE_SHIFT); + + /* map_pages is called with the RCU lock for reading (sleep isn't + * allowed) so just fall through to the more heavy-weight fault path. + */ + if (unlikely(!dma_resv_trylock(shmem->base.resv))) + return 0; + + if (unlikely(!drm_gem_shmem_fault_is_valid(obj, end_pgoff))) { + ret =3D VM_FAULT_SIGBUS; + goto out; + } + + /* Map a range of pages around the faulty address. */ + do { + pfn =3D page_to_pfn(pages[start_pgoff]); + ret =3D vmf_insert_pfn(vma, addr, pfn); + addr +=3D PAGE_SIZE; + } while (++start_pgoff <=3D end_pgoff && ret =3D=3D VM_FAULT_NOPAGE); + + out: + dma_resv_unlock(shmem->base.resv); + + return ret; +} + +static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf) +{ + struct vm_area_struct *vma =3D vmf->vma; + struct drm_gem_object *obj =3D vma->vm_private_data; + struct drm_gem_shmem_object *shmem =3D to_drm_gem_shmem_obj(obj); + struct page **pages =3D shmem->pages; pgoff_t page_offset; + unsigned long pfn; + vm_fault_t ret; =20 /* Offset to faulty address in the VMA (without the fake offset). */ page_offset =3D vmf->pgoff - vma->vm_pgoff; =20 dma_resv_lock(shmem->base.resv, NULL); =20 - if (page_offset >=3D num_pages || - drm_WARN_ON_ONCE(obj->dev, !shmem->pages) || - shmem->madv < 0) { + if (unlikely(!drm_gem_shmem_fault_is_valid(obj, page_offset))) { ret =3D VM_FAULT_SIGBUS; - } else { - page =3D shmem->pages[page_offset]; - - ret =3D vmf_insert_pfn(vma, vmf->address, page_to_pfn(page)); + goto out; } =20 + pfn =3D page_to_pfn(pages[page_offset]); + ret =3D vmf_insert_pfn(vma, vmf->address, pfn); + + out: dma_resv_unlock(shmem->base.resv); =20 return ret; @@ -632,6 +683,7 @@ static void drm_gem_shmem_vm_close(struct vm_area_struc= t *vma) } =20 const struct vm_operations_struct drm_gem_shmem_vm_ops =3D { + .map_pages =3D drm_gem_shmem_map_pages, .fault =3D drm_gem_shmem_fault, .open =3D drm_gem_shmem_vm_open, .close =3D drm_gem_shmem_vm_close, --=20 2.47.3