From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from va-1-111.ptr.blmpb.com (va-1-111.ptr.blmpb.com [209.127.230.111]) (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 C5C5D3B583B for ; Mon, 10 Aug 2026 12:24:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.127.230.111 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786364660; cv=none; b=t+gw0x2J4rg4UYvUcVa+pK3apmCinEmjZ5YL74dfl25abE9vOSFL+RA6r37QUomXB4N3c3m76fLKc/ZQU1hupx3SggdtqBJ/VgeuMsxGtwhzKAZBy9fAFn0Wn3euU0fzAv0zazvE2HN2C9lsyy1b6CJIThTJrFg69UxSXVspmpI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786364660; c=relaxed/simple; bh=EfJYEoeIj+mCjp87mw4swqkDiGUflYopMu+3ZYEHKXk=; h=To:Message-Id:Mime-Version:Content-Type:In-Reply-To:Cc:Subject: Date:References:From; b=WOGdQPnOWkiYIoN+kriAkN1D0xIGso77vZ1MeyxFCAs6z9eFUExFWbBh1RSHdFVMBHkrauh+XcN/U4+shP0TA4QwHi4Qd3WCZOORP7K8RpniNw25cX92J8cejfaf2Xlwz6sIW9OyqYl9jCeHESmStHw7sZB3XmiQFyCuwlW18Cw= 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=ASgSwMih; arc=none smtp.client-ip=209.127.230.111 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="ASgSwMih" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; s=2212171451; d=bytedance.com; t=1786364653; 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=ASgSwMihzIWUeCxi5uX8/oVqtNEpF9OANN0v5um83LWOXccOe/rN12Kxvt1QlZQEQ9I1NZ MJ+FCcLP5p2j7n6TrQjbHAdz4km/pmeS6XUmBuqjjqFikZwQ9MaeAWnmuriQW+i3EDe4G1 RowrgxetzsBgCxXFh3gWxlVaFAErV7TCWSI3KBm+xDxa3/06KDUbn5/zIqZGN4R9AFsTZv gGKgMBa2cU9bTJp4MzVKShu7RiI85L9mQzI5a6U5wb11DN8bdVwFI/yzcpdfqCRUHTDjBM xh0sgD9eo+kx/wGGXYaU2B+TxDmQzpkcq16MQBZ+DgtQczgDB3E0O3Zko3ee7Q== To: , , , , , , , , , , , Message-Id: <20260810122057.30447-7-lizhe.67@bytedance.com> 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 Content-Type: text/plain; charset=UTF-8 In-Reply-To: <20260810122057.30447-1-lizhe.67@bytedance.com> Cc: , , , , , Subject: [PATCH v10 6/8] string: introduce memcpy_nontemporal() Date: Mon, 10 Aug 2026 20:20:55 +0800 X-Lms-Return-Path: References: <20260810122057.30447-1-lizhe.67@bytedance.com> From: "Li Zhe" X-Original-From: Li Zhe Content-Transfer-Encoding: 7bit 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