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Howlett" , "Uladzislau Rezki" , "Miguel Ojeda" , "Boqun Feng" , "Gary Guo" , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , "Benno Lossin" , "Andreas Hindborg" , "Alice Ryhl" , "Trevor Gross" , "Daniel Almeida" , "Tamir Duberstein" , "Alexandre Courbot" , =?utf-8?q?Onur_=C3=96zkan?= , "David Airlie" , "Simona Vetter" , "John Hubbard" , "Alistair Popple" , "Timur Tabi" , , , , , "dri-devel" Subject: Re: [PATCH 2/6] gpu: nova-core: add NVKV encoder From: "Eliot Courtney" To: "Danilo Krummrich" , "Eliot Courtney" X-Mailer: aerc 0.21.0-0-g5549850facc2 References: <20260817-b4-nvkv-v1-0-b84db5e84b67@nvidia.com> <20260817-b4-nvkv-v1-2-b84db5e84b67@nvidia.com> In-Reply-To: X-ClientProxiedBy: TYCPR01CA0181.jpnprd01.prod.outlook.com (2603:1096:400:2b0::10) To DS0PR12MB6413.namprd12.prod.outlook.com (2603:10b6:8:ce::10) Precedence: bulk X-Mailing-List: nova-gpu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS0PR12MB6413:EE_|LVUPR12MB999161:EE_ X-MS-Office365-Filtering-Correlation-Id: 548ff955-9586-4532-0253-08df04471782 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|10070799003|366016|376014|7416014|1800799024|10067099003|6133799003|3023799007|22082099003|18002099003|4143699003|11063799006|56012099006; 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>>> + self.backing.reserve(num_entries, GFP_KERNEL)?; >>> + >>> + let spare =3D self.backing.spare_capacity_mut(); >>> + let dst =3D spare.as_mut_ptr().cast::(); >>> + >>> + // SAFETY: At least `bytes.len()` bytes of space are guarantee= d since `num_entries` >>> + // worth of space was just reserved. >>> + unsafe { core::ptr::copy_nonoverlapping(bytes.as_ptr(), dst, b= ytes.len()) }; >>> + >>> + let padding =3D num_entries * size_of::() - bytes.len(); >>> + if padding > 0 { >>> + // SAFETY: At least `num_entries * size_of::()` bytes= of space are guaranteed. >>> + unsafe { core::ptr::write_bytes(dst.add(bytes.len()), 0, p= adding) }; >>> + } >>> + >>> + // SAFETY: These bytes were just initialized and every bit pat= tern is valid for `u64`. >>> + unsafe { self.backing.inc_len(num_entries) }; >>> + >>> + Ok(()) >>> + } >> >> Ick! That's a lot of unsafe code. I think we can avoid this by using KVV= ec >> instead of KVVec, ideally in a new type that upholds the padding in= variant. >> >> Here's a diff of what I came up with; note that it also gets us rid of t= he >> unsafe in take_u32s() in the decoder by using zerocopy. >> >> (Technically it would also be possible to make Cursor operate on a byte = stream >> and let zerocopy to the rest, as all the take methods are fallible alrea= dy. But >> I think the invariant on EncodedStream makes sense.) > > Actually, I forgot to add the optimization you made back in, here's the p= roper > diff: > > (Also used T: IntoBytes as argument for extend_with_padding().) I sent the respin of this series using your EncodedStream idea but I think I should add you as Co-developed-by. If that makes sense I will add it plus your Signed-off-by (I think that's the right process?).