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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) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 8741F20002 X-Stat-Signature: 1m5c417s5udixj6czj1nag7iqdyczirt X-Rspam-User: X-HE-Tag: 1764576315-676636 X-HE-Meta: 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 M+yGle94 jKqni51X6UGstgadbq+hKkSdCikplxUAnjLRqK3VNIaJ6eBmyeCX+JpA8o5csFqr2kZg1oMSagUvRlNVlGR1DSbNJ03PAyZe27kI4ifTMiTrZgzLnIRL2GzMKjPQjMagESsi7JnIRcRbm3XqwsdaPIphH00EFDDs2S8HqmMAVsK9BJzU5QJ8KXiLV5Y5thgpOBYJ/qOTbZx0H5qGfhg3Uy9i+p0HfpSZ7pdELKrcDotEXNuxMQiOSgWXuW0BmjjcBY+9qvc+mnEFL08P0FUAvbZ8aux2n/VhyR+QL3JoS7+INe44xKdb0+ptKywUVsrtEit7psUh0ORnFdLoKgsZ/etjCwQDDcFnnae2KMWVkb47R3AEYpZTZfuYjDsttQ4dOKpTXaT1ETAzN7nUxWyrhW3qoiQ== 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 19:52:43 +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