From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 877EA414A1D; Mon, 6 Jul 2026 09:18:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783329539; cv=none; b=R+CM2J9r+Eif4JlPn/d6o5LcSM5WLG6kQ2vg0NT6bBmCKUiO3yhT0tXgZA98Xab2YgLvGadauSguhfWxyZ041lXapYMIblfnlYLzovsZq5+uoF+GiVxhKTTxqKk0d0NTuf29YdAZY6mNvOTiCT5xSEdKXhBNTQ3J2SR8Jlcvq2Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783329539; c=relaxed/simple; bh=0ZeyoyG9u0TeBIdAewzJeBAdmmO/wfP33IryoilEibs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=bYnp0BDbekgLYx9a99pkolDV7QjHZvDb7s63x/ub9P5bN/AG2wMvdrGuk2HELhATdNanObmztPxCAAOOuQekWmabcJWCODpj8FswRkKVKYskL7JFzm8mDGkymH3oiRXxgL5wr0eiEYT9UVpKDisaQrLsU3JDQr8Xpi4AbchAIPM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=oeOGQZW7; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="oeOGQZW7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7FD361F000E9; Mon, 6 Jul 2026 09:18:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; 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 Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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