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charset=UTF-8 To: , , , , , , , , , , , Date: Mon, 31 Aug 2026 19:16:36 +0800 Content-Transfer-Encoding: 7bit From: "Li Zhe" Subject: [PATCH v11 5/7] string: introduce memcpy_nontemporal() Message-Id: <20260831111638.76012-6-lizhe.67@bytedance.com> Mime-Version: 1.0 References: <20260831111638.76012-1-lizhe.67@bytedance.com> X-Original-From: Li Zhe In-Reply-To: <20260831111638.76012-1-lizhe.67@bytedance.com> X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 86E3880005 X-Stat-Signature: yyzn3a6gyp9k45tgxc5uind6sfmzqur6 X-Rspam-User: X-HE-Tag: 1788175182-473238 X-HE-Meta: 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 PJDSDDyk basTKXE/omF36oxsudcwj97yUwzlFibTHftAB7EdXPvzjcgKORQq+awL/9NnTN4Yhjs4WWPNy6R0BFdD2PHz5YPgb2AEEPV6NKXLUng9PO/Nl/HT1N1EiGE2mfZgfUWgjt9seONMrBiDeG+pCGnKAMdCJRF+ZcFTwwLMVIwcRscxXZtQyBLjFbFleQ4i/tPup2YtSfSkFUV60j2QXa1/eGUyS765QyzTWuSbRSh4ltnpI8DBZfXoKhDriHtS+6yG5pqU9LM4QmwN0Gm7qXn0gfGIbuYeL4mPO4mKYCELGvn5PRg8kKVm8KeTHyA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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