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t=1783329534; bh=ziaY5WXr4Dzm49LRmQEzdVWFHT5H2HonZXNfRetu1Io=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=oeOGQZW7+2lXYly6yT3KoxX63IAXYc6OlLNugLBcTJJexyCB1hvdNwP2WEncAgC60 ky7gotRrg58K7eNVbaelwPLeWMJzEyE/FCGCPAuSXCdgd/kW/NJ5VrRj/IL50dVwvF X3V+QvNBJtV87fn4jS8LfXt+YJhKRQMf2iKHBgaAd70USwfZPMD7FycUrxmNxqqqYA cHvBDSJC5YgI2loUMag3VeDCCpDkmmKh/qLUAHlyFngVm4s7bUAjflkHWuW5oawmgc aALChYa3yR6DyIq+diGzQMaCb4yRvtuHzkL22C2kkKa15xoMqYJxAnLmPI63DYrLDe llM3mTl8BD/CA== Message-ID: Date: Mon, 6 Jul 2026 11:18:48 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 6/8] string: introduce memcpy_nt() helpers To: Li Zhe , akpm@linux-foundation.org, apopple@nvidia.com, arnd@arndb.de, bp@alien8.de, dave.hansen@linux.intel.com, kees@kernel.org, mingo@redhat.com, rppt@kernel.org, tglx@kernel.org Cc: linux-arch@vger.kernel.org, linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org References: <20260701090553.62691-1-lizhe.67@bytedance.com> <20260701090553.62691-7-lizhe.67@bytedance.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 79C71A0005 X-Stat-Signature: 9g188j8yxy9mqcpud317hjedyysxy5hm X-HE-Tag: 1783329535-104111 X-HE-Meta: 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 DQMRMykv A32ofss6FuAbZ3U5zX5fGoOU/xcLUH9Cog2yvjz1veBJ+hXsuyJF2qHHQbrFzhh/7Ucrqp4oCG0xcpafABI+I9ZPop3FXZkwacCi7Lym0C8do1RBGokhyO19+7vGYuRW/wgWMFuZDKsrprmw6hd40O5m2gwXgF67PBFM/86wlyh+7GAG3xJmZgKWIJ5yNmGJfPSGFJwBFZ0YeZwdacjJrCSBr9HC93qtc3+gYP+Nqj0UvcaSW7fR2OsmjdjNSNxK8aHQVMf46FMNnYSfU+iTRXH74eNLBKrEDjkIVrs8yarcWDFQmULsq/VIZVy4JoOyz79sUxA3w8ne59AU7Bhb8AOAqTlOE2MBlKnfQ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/1/26 11:05, Li Zhe wrote: > Introduce memcpy_nt() and memcpy_nt_drain() for write-once copy sites > that want a named non-temporal copy primitive plus an explicit ordering > point. On x86, place the arch-visible wrapper in > arch/x86/include/asm/string_64.h and map it to the existing > memcpy_flushcache() backend plus sfence. Architectures that do not > override the helper fall back to memcpy() and a no-op drain in > include/linux/string.h. > > The immediate user is the ZONE_DEVICE template-copy path. That path > populates struct page descriptors in a write-once pattern, so most > destination cachelines are not expected to be reused immediately after > the copy. A regular cached memcpy() can therefore incur avoidable > write-allocate traffic and pollute the cache with data that has little > near-term reuse. > > This interface lets callers request that non-temporal-copy semantics > directly, while x86 simply reuses the existing memcpy_flushcache() > backend instead of adding another generic memcpy-like wrapper with > extra selection policy above it. > > Signed-off-by: Li Zhe > --- > arch/x86/include/asm/string_64.h | 16 ++++++++++++++++ > include/linux/string.h | 18 ++++++++++++++++++ > 2 files changed, 34 insertions(+) > > diff --git a/arch/x86/include/asm/string_64.h b/arch/x86/include/asm/string_64.h > index 4635616863f5..6f36abedc56a 100644 > --- a/arch/x86/include/asm/string_64.h > +++ b/arch/x86/include/asm/string_64.h > @@ -100,6 +100,22 @@ static __always_inline void memcpy_flushcache(void *dst, const void *src, size_t > } > __memcpy_flushcache(dst, src, cnt); > } > + > +#define __HAVE_ARCH_MEMCPY_NT 1 > +/* > + * Reuse the existing x86 flushcache backend as the nt copy primitive. > + * Callers pair it with memcpy_nt_drain() when later stores must be > + * ordered after the copy. > + */ > +static __always_inline void memcpy_nt(void *dst, const void *src, size_t cnt) > +{ > + memcpy_flushcache(dst, src, cnt); > +} In particular if you end up with a single function (that jsut requires a write memory barrier afterwards), please make this #define memcpy_nt memcpy_nt instead. -- Cheers, David