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Donenfeld" , Richard Henderson , linux-alpha@vger.kernel.org, Russell King , linux-arm-kernel@lists.infradead.org, Catalin Marinas , Huacai Chen , loongarch@lists.linux.dev, Geert Uytterhoeven , linux-m68k@lists.linux-m68k.org, Dinh Nguyen , Jonas Bonn , linux-openrisc@vger.kernel.org, Helge Deller , linux-parisc@vger.kernel.org, Michael Ellerman , linuxppc-dev@lists.ozlabs.org, Paul Walmsley , linux-riscv@lists.infradead.org, Heiko Carstens , linux-s390@vger.kernel.org, "David S. Miller" , sparclinux@vger.kernel.org Subject: [patch 19/38] kcsan: Replace get_cycles() usage References: <20260410120044.031381086@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-Rspam-User: X-Rspamd-Queue-Id: CA82F16000A X-Stat-Signature: sa4iejnddcuoq5qnd79dja8a1pbznfrh X-Rspamd-Server: rspam06 X-HE-Tag: 1775823605-951899 X-HE-Meta: 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 DRHiUCFT 82HsQ39+6zYY3Odgejfm+5GK5pnD1E5HikBh7cHqdIFycQ3W++FmB1PHmqt+cvGB7aqRwHt4M3sxC1SJQLewPstbkYtHvjqp9vVyr3vWsI8ApYgf4u//q6TwLHmdGgDZkYYuAh0LHJ4Nigi6WpMvnbCr4PS3B2Ehe656oT4fZ/V7301se1Z2Lpvf6inH21PSsGpsu8WbXfehB7MpxysGlysgRQydfW53CLqGkVoaP2hJo7VxA8/tgHOvCFqaalId20xy8CxpwHOgJwXwTwg7yQGAyzzG0558iOEgMMtSioi5/QxVg/7PmYzV2YI93MGjimOt8NQeUD9+qFC3UVXSEzqjanOIgsXATAawEDdHb1Jc/rLxUb4xl0WN9GOgA9swFqG6aiiAZXfJu6XNs+i6AaDzSFByMoDH3msEPqZbQ0Eul4n38Jf4h+v6wvF4IT8c0bL4T Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: KCSAN uses get_cycles() for two purposes: 1) Seeding the random state with get_cycles() is a historical leftover. 2) The microbenchmark uses get_cycles(), which provides an unit less counter value and is not guaranteed to be functional on all systems/platforms. Use random_get_entropy() for seeding the random state and ktime_get() which is universaly functional and provides at least a comprehensible unit. This is part of a larger effort to remove get_cycles() usage from non-architecture code. Signed-off-by: Thomas Gleixner Cc: Marco Elver Cc: Dmitry Vyukov Cc: kasan-dev@googlegroups.com --- kernel/kcsan/core.c | 2 +- kernel/kcsan/debugfs.c | 8 ++++---- 2 files changed, 5 insertions(+), 5 deletions(-) --- a/kernel/kcsan/core.c +++ b/kernel/kcsan/core.c @@ -798,7 +798,7 @@ void __init kcsan_init(void) BUG_ON(!in_task()); for_each_possible_cpu(cpu) - per_cpu(kcsan_rand_state, cpu) = (u32)get_cycles(); + per_cpu(kcsan_rand_state, cpu) = (u32)random_get_entropy(); /* * We are in the init task, and no other tasks should be running; --- a/kernel/kcsan/debugfs.c +++ b/kernel/kcsan/debugfs.c @@ -58,7 +58,7 @@ static noinline void microbenchmark(unsi { const struct kcsan_ctx ctx_save = current->kcsan_ctx; const bool was_enabled = READ_ONCE(kcsan_enabled); - u64 cycles; + ktime_t nsecs; /* We may have been called from an atomic region; reset context. */ memset(¤t->kcsan_ctx, 0, sizeof(current->kcsan_ctx)); @@ -70,16 +70,16 @@ static noinline void microbenchmark(unsi pr_info("%s begin | iters: %lu\n", __func__, iters); - cycles = get_cycles(); + nsecs = ktime_get(); while (iters--) { unsigned long addr = iters & ((PAGE_SIZE << 8) - 1); int type = !(iters & 0x7f) ? KCSAN_ACCESS_ATOMIC : (!(iters & 0xf) ? KCSAN_ACCESS_WRITE : 0); __kcsan_check_access((void *)addr, sizeof(long), type); } - cycles = get_cycles() - cycles; + nsecs = ktime_get() - nsecs; - pr_info("%s end | cycles: %llu\n", __func__, cycles); + pr_info("%s end | nsecs: %llu\n", __func__, nsecs); WRITE_ONCE(kcsan_enabled, was_enabled); /* restore context */