From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id CDFDDC55184 for ; Tue, 4 Aug 2026 17:06:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:Cc:List-Subscribe: List-Help:List-Post:List-Archive:List-Unsubscribe:List-Id: Content-Transfer-Encoding:MIME-Version:References:In-Reply-To:Message-Id:Date :Subject:To:From:Reply-To:Content-Type:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=PGV7xVqUZl6GPLTkEDpnrMoAZKyKWBMd77D9EJWaMLk=; b=HgrcF0XIGvrljo +XvoPAjfo5Gk9PkYHvII7Mw0MjOZmaQxthzWBl0xa6ys/eCCJzZ/aYWbA3MSTsG2Qf3fZuzRaP7vX CtsfA2yAia6uCYCVO4DMKtbLZajRQKkq0rcsyWZrSqf9A7EaM+QUGHER9JtBI+VRw+QVMWzpY64Z1 BximkRaWn2S7hZ3kkzbF31tP5TVY65OdGzI3vULfPW6hVPjzX0VzU38sjX0TyjycX/DTJTTk4LOsI IYLxLo7VT6IB8RAScnGgnHKBDwcso4X0SJtQs6DS4lSk1XFxH9ZOQlTWxHbPykokqZKrdT+KZGB6L pExAmIYUa3r0KQM23KAg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wrIap-00000002QZ3-1ytM; Tue, 04 Aug 2026 17:06:19 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wrIam-00000002QUs-2NKW for linux-arm-kernel@lists.infradead.org; Tue, 04 Aug 2026 17:06:17 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 447F01692; Tue, 4 Aug 2026 10:06:11 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 65D0B3F632; Tue, 4 Aug 2026 10:06:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1785863175; bh=sTGBfUvzjREhkQ+5bSeBU7PXovumMGH1x3aA9QLvhaU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=MHRubCVfa3deeHBCg1p5SSfZNv5FMcc4MMSes9V7j4Lwq3EMTq/b6bJu79CaKT1rM IMzW6uLoOMx3zMQwZXI81LW7KQA39VHdTJSLLZff661HzUTXa6ndhxxXJgqSqINtyN pVUjcUao2LahLskvQACErAkmzzRSiSsA/rD1XoFc= From: Mark Rutland To: linux-arm-kernel@lists.infradead.org Subject: [PATCH v2 14/20] arm64: percpu: Implement preemptible read/write ops Date: Tue, 4 Aug 2026 18:04:57 +0100 Message-Id: <20260804170503.3513916-15-mark.rutland@arm.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20260804170503.3513916-1-mark.rutland@arm.com> References: <20260804170503.3513916-1-mark.rutland@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260804_100616_853049_4B489CB2 X-CRM114-Status: GOOD ( 10.76 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, vladimir.murzin@arm.com, ryan.roberts@arm.com, peterz@infradead.org, catalin.marinas@arm.com, david.laight.linux@gmail.com, stable@vger.kernel.org, ruanjinjie@huawei.com, james.morse@arm.com, yang@os.amperecomputing.com, cl@gentwo.org, maz@kernel.org, david@kernel.org, ljs@kernel.org, will@kernel.org, ardb@kernel.org Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Use the PCPU GPR infrastructure to implement preemptible this_cpu_read() and this_cpu_write(). This change means that this_cpu_read() will always use a plain LDR, even in LTO configurations where READ_ONCE() will use LDA[P]R. Using plain LDR is preferable, given that the rationale for using LDA[P]R in READ_ONCE() was to retain address dependencies against values written by other CPUs, which isn't expected usage for this_cpu_read(). Using plain LDR will enforce fewer ordering constraints. Test case: | void outline_this_cpu_write_u64(u64 __percpu *p, u64 v) | { | this_cpu_write(*p, v); | } Generated code before this patch (v7.2-rc4): | : | paciasp | stp x29, x30, [sp, #-16]! | mrs x2, sp_el0 | mov x29, sp | ldr w3, [x2, #8] | add w3, w3, #0x1 | str w3, [x2, #8] | mrs x3, tpidr_el1 | str x1, [x0, x3] | ldr x0, [x2, #8] | sub x0, x0, #0x1 | str w0, [x2, #8] | cbz x0, 1f | ldr x0, [x2, #8] | cbnz x0, 2f | 1: bl preempt_schedule_notrace | 2: ldp x29, x30, [sp], #16 | autiasp | ret Generated code after this patch: | : | mrs x2, sp_el0 | mov w3, #0x7c60 | strh w3, [x2, #20] | mrs x3, tpidr_el1 | str x1, [x0, x3] | strh wzr, [x2, #20] | ret Signed-off-by: Mark Rutland Cc: Ada Couprie Diaz Cc: Ard Biesheuvel Cc: Catalin Marinas Cc: James Morse Cc: Jinjie Ruan Cc: Marc Zyngier Cc: Peter Zijlstra Cc: Vladimir Murzin Cc: Will Deacon Cc: Yang Shi --- arch/arm64/include/asm/percpu.h | 79 ++++++++++++++++++++++++--------- 1 file changed, 58 insertions(+), 21 deletions(-) diff --git a/arch/arm64/include/asm/percpu.h b/arch/arm64/include/asm/percpu.h index 8b4c9ea05d4e6..a094c137d797f 100644 --- a/arch/arm64/include/asm/percpu.h +++ b/arch/arm64/include/asm/percpu.h @@ -128,15 +128,42 @@ static inline unsigned long __kern_my_cpu_offset(void) #define __my_cpu_offset __kern_my_cpu_offset() #endif -#define PERCPU_RW_OPS(sz) \ -static inline unsigned long __percpu_read_##sz(void *ptr) \ -{ \ - return READ_ONCE(*(u##sz *)ptr); \ -} \ - \ -static inline void __percpu_write_##sz(void *ptr, unsigned long val) \ -{ \ - WRITE_ONCE(*(u##sz *)ptr, (u##sz)val); \ +#define PERCPU_RW_OPS(w, sfx, sz) \ +static inline unsigned long __percpu_read_##sz(void __percpu *pcp) \ +{ \ + u16 *gprs = ¤t_thread_info()->pcpu_gprs; \ + unsigned long off; \ + unsigned long val; \ + \ + asm volatile( \ + __PCPU_GPRS_BEGIN_OFFSET("%[gprs]", "%[pcp]", "%[off]") \ + " ldr" #sfx "\t%" #w "[val], [%[pcp], %[off]]\n" \ + __PCPU_GPRS_END("%[gprs]") \ + : [gprs] "=Qo" (*gprs), \ + [off] "=&r" (off), \ + [val] "=&r" (val) \ + : [pcp] "r" (pcp) \ + : "memory" \ + ); \ + \ + return val; \ +} \ + \ +static inline void __percpu_write_##sz(void __percpu *pcp, u##sz val) \ +{ \ + u16 *gprs = ¤t_thread_info()->pcpu_gprs; \ + unsigned long off; \ + \ + asm volatile( \ + __PCPU_GPRS_BEGIN_OFFSET("%[gprs]", "%[pcp]", "%[off]") \ + " str" #sfx "\t%" #w "[val], [%[pcp], %[off]]\n" \ + __PCPU_GPRS_END("%[gprs]") \ + : [gprs] "=Qo" (*gprs), \ + [off] "=&r" (off) \ + : [pcp] "r" (pcp), \ + [val] "r" (val) \ + : "memory" \ + ); \ } #define __PERCPU_OP_CASE(w, sfx, name, sz, op_llsc, op_lse) \ @@ -196,10 +223,10 @@ __percpu_##name##_return_case_##sz(void *ptr, unsigned long val) \ __PERCPU_RET_OP_CASE(w, , name, 32, op_llsc, op_lse) \ __PERCPU_RET_OP_CASE( , , name, 64, op_llsc, op_lse) -PERCPU_RW_OPS(8) -PERCPU_RW_OPS(16) -PERCPU_RW_OPS(32) -PERCPU_RW_OPS(64) +PERCPU_RW_OPS(w, b, 8) +PERCPU_RW_OPS(w, h, 16) +PERCPU_RW_OPS(w, , 32) +PERCPU_RW_OPS( , , 64) /* * Use value-returning atomics for CPU-local ops as they are more likely @@ -245,23 +272,33 @@ PERCPU_RET_OP(add, add, ldadd) __retval; \ }) +#define _pcp_wrap(op, pcp, ...) \ +({ \ + op(&(pcp), __VA_ARGS__); \ +}) + +#define _pcp_wrap_return(op, pcp, args...) \ +({ \ + (typeof(pcp))op(&(pcp), ##args); \ +}) + #define this_cpu_read_1(pcp) \ - _pcp_protect_return(__percpu_read_8, pcp) + _pcp_wrap_return(__percpu_read_8, pcp) #define this_cpu_read_2(pcp) \ - _pcp_protect_return(__percpu_read_16, pcp) + _pcp_wrap_return(__percpu_read_16, pcp) #define this_cpu_read_4(pcp) \ - _pcp_protect_return(__percpu_read_32, pcp) + _pcp_wrap_return(__percpu_read_32, pcp) #define this_cpu_read_8(pcp) \ - _pcp_protect_return(__percpu_read_64, pcp) + _pcp_wrap_return(__percpu_read_64, pcp) #define this_cpu_write_1(pcp, val) \ - _pcp_protect(__percpu_write_8, pcp, (unsigned long)(val)) + _pcp_wrap(__percpu_write_8, pcp, (unsigned long)(val)) #define this_cpu_write_2(pcp, val) \ - _pcp_protect(__percpu_write_16, pcp, (unsigned long)(val)) + _pcp_wrap(__percpu_write_16, pcp, (unsigned long)(val)) #define this_cpu_write_4(pcp, val) \ - _pcp_protect(__percpu_write_32, pcp, (unsigned long)(val)) + _pcp_wrap(__percpu_write_32, pcp, (unsigned long)(val)) #define this_cpu_write_8(pcp, val) \ - _pcp_protect(__percpu_write_64, pcp, (unsigned long)(val)) + _pcp_wrap(__percpu_write_64, pcp, (unsigned long)(val)) #define this_cpu_add_1(pcp, val) \ _pcp_protect(__percpu_add_case_8, pcp, val) -- 2.30.2