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Wed, 26 Nov 2025 05:49:30 +0000 (UTC) Date: Wed, 26 Nov 2025 15:49:26 +1000 From: Brendan Shephard To: Alice Ryhl Cc: dakr@kernel.org, acourbot@nvidia.com, joelagnelf@nvidia.com, jhubbard@nvidia.com, airlied@gmail.com, rust-for-linux@vger.kernel.org, nouveau@lists.freedesktop.org, brendan.shephard@gmail.com Subject: Re: [PATCH 1/1] drm: nova: Align GEM memory allocation to system page size Message-ID: References: <98227EBD-92F7-40FC-A5A4-3FF3780FB2CB@bne-home.net> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Authority-Info: v=2.4 cv=QJFlhwLL c=1 sm=1 tr=0 ts=692694ee cx=c_apl:c_pps a=qkKslKyYc0ctBTeLUVfTFg==:117 a=kj9zAlcOel0A:10 a=6UeiqGixMTsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VwQbUJbxAAAA:8 a=JppZAXPjAAAA:8 a=Bcv9xwsS2OVvdwMGJkkA:9 a=CjuIK1q_8ugA:10 a=mTXuAFqUwmiQvsSFmwXH:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTI2MDA0NSBTYWx0ZWRfXwUljMWoC9SaO 9OUPodwFYNL45lZ2XiXrGYTsNRbNiUcLLcJio18UjkfsN4qpXKalXHVcTAhcteQSNJ5M/LbZ8Sr c8SjLMIOVfvwfCst201nsiNvnAPySA/wo+WP40r0qP64Tya4RfqmAaiVzOV5uOKKStOEbhSuWUR 4FQZoVva+NUfdzoNHExVXv8b/e7WnpYhL/KlNrHPKxIJxFEdh+bYZOXwW6s5HeG+0OOe1/ugHMg 2mbBaJl0pX0Z7IuYFC+dmPTkp/WOENfcdfDURFha2xszQSUFydBGyxuCKhROShqPyv2a3dwZ1+4 xz9ulfukx26Iz06QtFT X-Proofpoint-ORIG-GUID: KBvgApPOmXImsYQa4J90rS2jHxfwfwf9 X-Proofpoint-GUID: KBvgApPOmXImsYQa4J90rS2jHxfwfwf9 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-11-25_02,2025-11-25_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 mlxlogscore=452 clxscore=1030 malwarescore=0 mlxscore=0 bulkscore=0 suspectscore=0 phishscore=0 adultscore=0 classifier=spam authscore=0 adjust=0 reason=mlx scancount=1 engine=8.22.0-2510240001 definitions=main-2511260045 X-JNJ: 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 On Tue, Nov 25, 2025 at 09:23:59AM +0000, Alice Ryhl wrote: > On Fri, Nov 21, 2025 at 02:04:28PM +1000, bshephar@bne-home.net wrote: > > impl NovaObject { > > /// Create a new DRM GEM object. > > pub(crate) fn new(dev: &NovaDevice, size: usize) -> Result>> { > > - let aligned_size = size.next_multiple_of(1 << 12); > > - > > - if size == 0 || size > aligned_size { > > + // Check for 0 size or potential usize overflow before calling page_align > > + if size == 0 || size > usize::MAX - PAGE_SIZE + 1 { > > Maybe this should use isize::MAX as the maximum size instead? That's a > pretty common maximum size for allocations in Rust and big enough for > everyone. > > Alice Thanks for the review Alice. I used usize here because the page_align() function specifically mentions that the provided value should not overflow a ['usize']. https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/rust/kernel/page.rs#n30 I don't think that alone needs to be the deciding factor, but it's worth expressing why I made that decision to begin with. Happy to hear your thoughts, and if you still feel isize::MAX is more appropriate given this information. Brendan