From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from va-1-115.ptr.blmpb.com (va-1-115.ptr.blmpb.com [209.127.230.115]) (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 C0B6039FCCA for ; Mon, 31 Aug 2026 11:19:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.127.230.115 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788175184; cv=none; b=gABie2dtUGeYiVbrrjYdTaDtxvUZsiXp082lwLkYVDlQgBwSXDbCFh00MSxQcqhr4rhi65IfH5c8pjoCp0pXK+roj6aGMvuhJEorLDdxX0WjzI07RtA9fI7qMsb3UNE+T2o/aMRbNsm8wyN5vuOCXCiREf7rPp1wWmwNxEkIbcs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788175184; c=relaxed/simple; bh=EfJYEoeIj+mCjp87mw4swqkDiGUflYopMu+3ZYEHKXk=; h=Mime-Version:References:Cc:Content-Type:Subject:Date:Message-Id: To:From:In-Reply-To; b=lzVFAGHJ7uvafy5/NByD3x0NlVfFtFlQ7lGeAQvSesJd5bywGlEuIFEZPiX0QfIvibELOSVqW2BvPQOOpBVQTmSPLfLA+KrC880+UM8WIlZx4VQspTFGzWaDTNwf3icIRBMScCNJShTMyUOY2CcWYCIhibQN8X5gTl9Yn8urSII= 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=WKffv7O1; arc=none smtp.client-ip=209.127.230.115 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="WKffv7O1" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; s=2212171451; d=bytedance.com; t=1788175177; 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=WKffv7O1sbRM1osAyUrOPj/LcydRazz9CfJLkbVjpmCjPFMacahd0G5PQSYJHm4qKtCnuH QMuTPfJyQ4UjmUO9r8iaNPmXzxu3JIN19GsSQZR3oqwutp6VWYc4KBM05Cy3PdjipoPAAm 4QCcIqvVZ87FFuju5c2m3mLZTr3nLm2eaYhZKrNYgwl7ZICl5LahpjZEx1RHQNGOfWNLNq 3PNxUtelRsAzeZQyZE6onsENE33a6A47eArJ5+BimgZRRmLVf+x58bN9SiCO1drI9WpNZq dqVb6LspxuL2e9iy1zbvq5owwS/bs2HBwdxvoGj3MtjrZdnrjfSZp+6luKxp2A== Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.45.2 X-Original-From: Li Zhe References: <20260831111638.76012-1-lizhe.67@bytedance.com> Cc: , , , , , X-Lms-Return-Path: Content-Type: text/plain; charset=UTF-8 Subject: [PATCH v11 5/7] string: introduce memcpy_nontemporal() Date: Mon, 31 Aug 2026 19:16:36 +0800 Message-Id: <20260831111638.76012-6-lizhe.67@bytedance.com> Content-Transfer-Encoding: 7bit To: , , , , , , , , , , , From: "Li Zhe" In-Reply-To: <20260831111638.76012-1-lizhe.67@bytedance.com> 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