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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 1668E17E12D5; Fri, 5 Dec 2025 19:22:36 +0100 (CET) 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 v13 02/10] drm/shmem-helper: Map huge pages in fault handler Date: Fri, 5 Dec 2025 19:22:23 +0100 Message-ID: <20251205182231.194072-3-loic.molinari@collabora.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20251205182231.194072-1-loic.molinari@collabora.com> References: <20251205182231.194072-1-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 Attempt a PMD sized PFN insertion into the VMA if the faulty address of the fault handler is part of a huge page. On builds with CONFIG_TRANSPARENT_HUGEPAGE enabled, if the mmap() user address is PMD size aligned, if the GEM object is backed by shmem buffers on mountpoints setting the 'huge=3D' option and if the shmem backing store manages to allocate a huge folio, CPU mapping would then benefit from significantly increased memcpy() performance. When these conditions are met on a system with 2 MiB huge pages, an aligned copy of 2 MiB would raise a single page fault instead of 4096. v4: - implement map_pages instead of huge_fault v6: - get rid of map_pages handler for now (keep it for another series along with arm64 contpte support) v11: - remove page fault validity check helper - rename drm_gem_shmem_map_pmd() to drm_gem_shmem_try_map_pmd() - add Boris R-b v12: - move up ret var decl in fault handler to minimize diff Signed-off-by: Lo=C3=AFc Molinari Reviewed-by: Boris Brezillon --- drivers/gpu/drm/drm_gem_shmem_helper.c | 35 +++++++++++++++++++++++--- 1 file changed, 31 insertions(+), 4 deletions(-) diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_g= em_shmem_helper.c index e47ab3ebb5c2..e67216cbb469 100644 --- a/drivers/gpu/drm/drm_gem_shmem_helper.c +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c @@ -567,6 +567,26 @@ int drm_gem_shmem_dumb_create(struct drm_file *file, s= truct drm_device *dev, } EXPORT_SYMBOL_GPL(drm_gem_shmem_dumb_create); =20 +static bool drm_gem_shmem_try_map_pmd(struct vm_fault *vmf, unsigned long = addr, + struct page *page) +{ +#ifdef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP + unsigned long pfn =3D page_to_pfn(page); + unsigned long paddr =3D pfn << PAGE_SHIFT; + bool aligned =3D (addr & ~PMD_MASK) =3D=3D (paddr & ~PMD_MASK); + + if (aligned && + pmd_none(*vmf->pmd) && + folio_test_pmd_mappable(page_folio(page))) { + pfn &=3D PMD_MASK >> PAGE_SHIFT; + if (vmf_insert_pfn_pmd(vmf, pfn, false) =3D=3D VM_FAULT_NOPAGE) + return true; + } +#endif + + return false; +} + static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf) { struct vm_area_struct *vma =3D vmf->vma; @@ -574,8 +594,9 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *= vmf) struct drm_gem_shmem_object *shmem =3D to_drm_gem_shmem_obj(obj); loff_t num_pages =3D obj->size >> PAGE_SHIFT; vm_fault_t ret; - struct page *page; + struct page **pages =3D shmem->pages; pgoff_t page_offset; + unsigned long pfn; =20 /* Offset to faulty address in the VMA. */ page_offset =3D vmf->pgoff - vma->vm_pgoff; @@ -586,12 +607,18 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault= *vmf) drm_WARN_ON_ONCE(obj->dev, !shmem->pages) || shmem->madv < 0) { ret =3D VM_FAULT_SIGBUS; - } else { - page =3D shmem->pages[page_offset]; + goto out; + } =20 - ret =3D vmf_insert_pfn(vma, vmf->address, page_to_pfn(page)); + if (drm_gem_shmem_try_map_pmd(vmf, vmf->address, pages[page_offset])) { + ret =3D VM_FAULT_NOPAGE; + 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; --=20 2.47.3