linux-kernel - [PATCH 1/5] asm-generic: add smp_vcond_load

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Message-ID: <20241105183041.1531976-2-harisokn@amazon.com>
Date: Tue, 5 Nov 2024 12:30:37 -0600
From: Haris Okanovic <harisokn@...zon.com>
To: <ankur.a.arora@...cle.com>, <catalin.marinas@....com>
CC: <linux-pm@...r.kernel.org>, <kvm@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
	<will@...nel.org>, <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>, <x86@...nel.org>, <hpa@...or.com>,
	<pbonzini@...hat.com>, <wanpengli@...cent.com>, <vkuznets@...hat.com>,
	<rafael@...nel.org>, <daniel.lezcano@...aro.org>, <peterz@...radead.org>,
	<arnd@...db.de>, <lenb@...nel.org>, <mark.rutland@....com>,
	<harisokn@...zon.com>, <mtosatti@...hat.com>, <sudeep.holla@....com>,
	<cl@...two.org>, <misono.tomohiro@...itsu.com>, <maobibo@...ngson.cn>,
	<joao.m.martins@...cle.com>, <boris.ostrovsky@...cle.com>,
	<konrad.wilk@...cle.com>
Subject: [PATCH 1/5] asm-generic: add smp_vcond_load_relaxed()

Relaxed poll until desired mask/value is observed at the specified
address or timeout.

This macro is a specialization of the generic smp_cond_load_relaxed(),
which takes a simple mask/value condition (vcond) instead of an
arbitrary expression. It allows architectures to better specialize the
implementation, e.g. to enable wfe() polling of the address on arm.

Signed-off-by: Haris Okanovic <harisokn@...zon.com>
---
 include/asm-generic/barrier.h | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index d4f581c1e21d..112027eabbfc 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -256,6 +256,31 @@ do {									\
 })
 #endif
 
+/**
+ * smp_vcond_load_relaxed() - (Spin) wait until an expected value at address
+ * with no ordering guarantees. Spins until `(*addr & mask) == val` or
+ * `nsecs` elapse, and returns the last observed `*addr` value.
+ *
+ * @nsecs: timeout in nanoseconds
+ * @addr: pointer to an integer
+ * @mask: a bit mask applied to read values
+ * @val: Expected value with mask
+ */
+#ifndef smp_vcond_load_relaxed
+#define smp_vcond_load_relaxed(nsecs, addr, mask, val) ({	\
+	const u64 __start = local_clock_noinstr();		\
+	u64 __nsecs = (nsecs);					\
+	typeof(addr) __addr = (addr);				\
+	typeof(*__addr) __mask = (mask);			\
+	typeof(*__addr) __val = (val);				\
+	typeof(*__addr) __cur;					\
+	smp_cond_load_relaxed(__addr, (				\
+		(VAL & __mask) == __val ||			\
+		local_clock_noinstr() - __start > __nsecs	\
+	));							\
+})
+#endif
+
 /**
  * smp_cond_load_acquire() - (Spin) wait for cond with ACQUIRE ordering
  * @ptr: pointer to the variable to wait on
-- 
2.34.1