From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from va-1-112.ptr.blmpb.com (va-1-112.ptr.blmpb.com [209.127.230.112]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D37C03FF8A7 for ; Mon, 27 Jul 2026 12:37:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.127.230.112 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785155854; cv=none; b=etXI5vRCDipNM9wphOGtml/6nTBZISTtYk+iXkxAdY9ZenuKGZorLt57ybOfk09zcXqsxG0PbN8lgUl4uV700fbv6Xye0t95wZNgEHgXlxs4wSoDecM61aYgi1SNvUy5TuALEmgCiYJxQxyK/f0LSwgs7fCc/qkyut9XjR8Qlb8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785155854; c=relaxed/simple; bh=EfJYEoeIj+mCjp87mw4swqkDiGUflYopMu+3ZYEHKXk=; h=Content-Type:From:Message-Id:Mime-Version:References:Cc:Date:To: Subject:In-Reply-To; b=CClCp9bBmMVhcfIPHornCVvocRzEw3LUTaV3gnUBmwp4kuKSHruNBvyWolMOXNay3g3BxhSzIpwyP4B3c9So+9dcw32XYCdCiYp0aBP+oQS23lKVD3PzwbJDKyAvEfFvuTdA6XS8DYu5zHm69viqT8og1eK6EW/2g6+/o8z1Ano= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=bytedance.com; spf=pass smtp.mailfrom=bytedance.com; dkim=pass (2048-bit key) header.d=bytedance.com header.i=@bytedance.com header.b=GSFclNsg; arc=none smtp.client-ip=209.127.230.112 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=bytedance.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=bytedance.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=bytedance.com header.i=@bytedance.com header.b="GSFclNsg" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; s=2212171451; d=bytedance.com; t=1785155848; h=from:subject: mime-version:from:date:message-id:subject:to:cc:reply-to:content-type: mime-version:in-reply-to:message-id; bh=vLcTykUrPpLwId0/keP/ANeuOzuTtpvXBhogtTbcEIQ=; b=GSFclNsglDCGfGJRdtvcdheDSfTeFeYjIqDZSrsm9iA6KPjhFnN1yvwWa8BPA5rIOeiPL5 3miHH4FA51hOjkqDaFULrWOnHQNwn4StQFiyXXL9dQ8r7ugtRtraI6gLN9zGOZt62oh34b DGBBtVqtZUnN/nMEjlsx3N63YjfLxCyu5ibwHQb3h1w5kMsV3cSP9N+Iuh9e8mEKUbXpXy K+KVqNFJtpj7mLXz4PqblUTlBThRsl2GS8P+9VOALLVZbPrCNg7FucUWP0ubCbVGGIXFnX e868MmEVIj9iEwGoldWT5e+CJzWgip2Grj3SbbCcSPH5fJXLLdRIr0eWmehtnQ== Content-Type: text/plain; charset=UTF-8 From: "Li Zhe" Message-Id: <20260727123429.5673-7-lizhe.67@bytedance.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260727123429.5673-1-lizhe.67@bytedance.com> X-Mailer: git-send-email 2.45.2 Cc: , , , , , Date: Mon, 27 Jul 2026 20:34:26 +0800 Content-Transfer-Encoding: 7bit X-Lms-Return-Path: To: , , , , , , , , , , , Subject: [PATCH v8 6/9] string: introduce memcpy_nontemporal() In-Reply-To: <20260727123429.5673-1-lizhe.67@bytedance.com> X-Original-From: Li Zhe Introduce memcpy_nontemporal() for write-once copy sites that want a named non-temporal copy primitive. On x86_64, override the helper in arch/x86/include/asm/string_64.h using the usual self-macro pattern, next to the existing memcpy_flushcache() backend that memcpy_nontemporal() wraps. include/linux/string.h provides the generic memcpy_nontemporal() fallback as #define memcpy_nontemporal(dst, src, len) \ ((void)memcpy(dst, src, len)) instead of an inline wrapper, so architectures without a specialized backend keep the usual memcpy() FORTIFY coverage when the compiler can still see object sizes at the original call site. It also makes the memcpy_nontemporal() API uniformly void, matching memcpy_flushcache() and the x86 backend, so callers cannot accidentally depend on a return value on fallback architectures. memcpy_nontemporal() is only a copy primitive. It does not imply a drain or a publication barrier. Callers that use it before a producer-consumer or device-visible handoff must provide the required ordering at that handoff point. The immediate user is the ZONE_DEVICE template-copy path. It populates struct page descriptors in a write-once pattern, so a regular cached memcpy() can incur avoidable write-allocate traffic and cache pollution for data with little near-term reuse. Signed-off-by: Li Zhe --- arch/x86/include/asm/string_64.h | 12 ++++++++++++ include/linux/string.h | 13 +++++++++++++ 2 files changed, 25 insertions(+) diff --git a/arch/x86/include/asm/string_64.h b/arch/x86/include/asm/string_64.h index 4635616863f5..21ae515ae35a 100644 --- a/arch/x86/include/asm/string_64.h +++ b/arch/x86/include/asm/string_64.h @@ -100,6 +100,18 @@ static __always_inline void memcpy_flushcache(void *dst, const void *src, size_t } __memcpy_flushcache(dst, src, cnt); } + +#define memcpy_nontemporal memcpy_nontemporal +/* + * Reuse the existing x86 flushcache backend as the non-temporal copy + * primitive. + */ +static __always_inline void memcpy_nontemporal(void *dst, const void *src, + size_t cnt) +{ + memcpy_flushcache(dst, src, cnt); +} + #endif #endif /* __KERNEL__ */ diff --git a/include/linux/string.h b/include/linux/string.h index 5702daca4326..6cb5cdd01158 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -278,6 +278,19 @@ static inline void memcpy_flushcache(void *dst, const void *src, size_t cnt) } #endif +#ifndef memcpy_nontemporal +/* + * memcpy_nontemporal() requests a non-temporal copy when the + * architecture has a suitable backend. Architectures without a + * specialized backend fall back to memcpy(). Keep this as a + * function-like macro so the compiler can still see the original + * memcpy() call site and preserve the usual FORTIFY coverage when + * object sizes remain visible there, while keeping the API void. + */ +#define memcpy_nontemporal(dst, src, len) \ + ((void)memcpy(dst, src, len)) +#endif + void *memchr_inv(const void *s, int c, size_t n); char *strreplace(char *str, char old, char new); -- 2.20.1