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charset=UTF-8 Subject: [PATCH v8 6/9] string: introduce memcpy_nontemporal() X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 62131100005 X-Stat-Signature: eijtqyqkon1p3m7zoihu66sm5gpdjxxr X-HE-Tag: 1785155853-944928 X-HE-Meta: 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 SJTv1fxN /6TTtWtkpC7dH9hZunXC+mvlpCLysBnshtS12WkVlmZwiGsN9KHY/IfKfY9jNKg2pLdBnJSZnkqA/PLCuo09uTR7jYFMO3W96Eyv6ug1vbYjJT2YtjGCN02sawnFVihABrEX5pYJG4Y7DvIvlElWHBk8aSC1DXgRgx+685b/lvFPZUBOAr2e2ENEb5OwjxaP/8yNW4H1kDdxur/pyxH/K5j3cCU65Aj4yk73Z6pLEDm9QQWH6hfbGG19qKllq7s1vc7sLwh+77iV6q4+R20t2HhM/2mYq0V0iw7Xmf6OMehjkBUW/h3KPY8dhXg== 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