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Mon, 1 Dec 2025 09:05:11 +0100 (CET) Date: Mon, 1 Dec 2025 09:05:07 +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 01/10] drm/shmem-helper: Simplify page offset calculation in fault handler Message-ID: <20251201090507.1ee10c65@fedora> In-Reply-To: <20251128185252.3092-2-loic.molinari@collabora.com> References: <20251128185252.3092-1-loic.molinari@collabora.com> <20251128185252.3092-2-loic.molinari@collabora.com> Organization: Collabora X-Mailer: Claws Mail 4.3.1 (GTK 3.24.51; x86_64-redhat-linux-gnu) Precedence: bulk X-Mailing-List: linux-doc@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 Fri, 28 Nov 2025 19:52:43 +0100 Lo=C3=AFc Molinari wrote: > For a fault at address addr, the page offset is > page_offset =3D (vmf->address - vma->vm_start) >> PAGE_SHIFT > =3D ((addr & PAGE_MASK) - vma->vm_start) >> PAGE_SHIFT > =3D (addr - vma->vm_start) >> PAGE_SHIFT >=20 > Since the faulty logical page offset based on VMA is > vmf->pgoff =3D vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT) >=20 > We can slightly simplify the calculation using > page_offset =3D vmf->pgoff - vma->vm_pgoff >=20 > Signed-off-by: Lo=C3=AFc Molinari Reviewed-by: Boris Brezillon One nit below > --- > drivers/gpu/drm/drm_gem_shmem_helper.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) >=20 > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm= _gem_shmem_helper.c > index dc94a27710e5..be89be1c804c 100644 > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c > @@ -577,8 +577,8 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault= *vmf) > struct page *page; > pgoff_t page_offset; > =20 > - /* We don't use vmf->pgoff since that has the fake offset */ > - page_offset =3D (vmf->address - vma->vm_start) >> PAGE_SHIFT; > + /* Offset to faulty address in the VMA (without the fake offset). */ It's weird to say "without the fake offset" here, because IIUC, both vmf->pgoff and vma->vm_pgoff contain the fake offset. And that's fine, the problem really is when one of the subtraction operand is not relative to the fake offset. > + page_offset =3D vmf->pgoff - vma->vm_pgoff; > =20 > dma_resv_lock(shmem->base.resv, NULL); > =20