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git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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e5cb94ba5f
Ben reports that when running with CONFIG_DEBUG_PREEMPT, using
__arch_counter_get_cntvct_stable() results in well deserves warnings,
as we access a per-CPU variable without preemption disabled.
Fix the issue by disabling preemption on reading the counter. We can
probably do a lot better by not disabling preemption on systems that
do not require horrible workarounds to return a valid counter value,
but this plugs the issue for the time being.
Fixes: 29cc0f3aa7 ("arm64: Force the use of CNTVCT_EL0 in __delay()")
Reported-by: Ben Horgan <ben.horgan@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/aZw3EGs4rbQvbAzV@e134344.arm.com
Tested-by: Ben Horgan <ben.horgan@arm.com>
Tested-by: André Draszik <andre.draszik@linaro.org>
Signed-off-by: Will Deacon <will@kernel.org>
85 lines
2.1 KiB
C
85 lines
2.1 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Delay loops based on the OpenRISC implementation.
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*
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* Copyright (C) 2012 ARM Limited
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*
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* Author: Will Deacon <will.deacon@arm.com>
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*/
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#include <linux/delay.h>
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#include <linux/init.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/timex.h>
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#include <clocksource/arm_arch_timer.h>
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#define USECS_TO_CYCLES(time_usecs) \
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xloops_to_cycles((time_usecs) * 0x10C7UL)
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static inline unsigned long xloops_to_cycles(unsigned long xloops)
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{
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return (xloops * loops_per_jiffy * HZ) >> 32;
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}
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/*
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* Force the use of CNTVCT_EL0 in order to have the same base as WFxT.
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* This avoids some annoying issues when CNTVOFF_EL2 is not reset 0 on a
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* KVM host running at EL1 until we do a vcpu_put() on the vcpu. When
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* running at EL2, the effective offset is always 0.
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*
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* Note that userspace cannot change the offset behind our back either,
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* as the vcpu mutex is held as long as KVM_RUN is in progress.
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*/
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static cycles_t notrace __delay_cycles(void)
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{
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guard(preempt_notrace)();
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return __arch_counter_get_cntvct_stable();
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}
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void __delay(unsigned long cycles)
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{
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cycles_t start = __delay_cycles();
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if (alternative_has_cap_unlikely(ARM64_HAS_WFXT)) {
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u64 end = start + cycles;
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/*
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* Start with WFIT. If an interrupt makes us resume
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* early, use a WFET loop to complete the delay.
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*/
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wfit(end);
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while ((__delay_cycles() - start) < cycles)
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wfet(end);
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} else if (arch_timer_evtstrm_available()) {
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const cycles_t timer_evt_period =
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USECS_TO_CYCLES(ARCH_TIMER_EVT_STREAM_PERIOD_US);
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while ((__delay_cycles() - start + timer_evt_period) < cycles)
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wfe();
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}
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while ((__delay_cycles() - start) < cycles)
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cpu_relax();
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}
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EXPORT_SYMBOL(__delay);
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inline void __const_udelay(unsigned long xloops)
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{
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__delay(xloops_to_cycles(xloops));
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}
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EXPORT_SYMBOL(__const_udelay);
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void __udelay(unsigned long usecs)
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{
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__const_udelay(usecs * 0x10C7UL); /* 2**32 / 1000000 (rounded up) */
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}
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EXPORT_SYMBOL(__udelay);
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void __ndelay(unsigned long nsecs)
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{
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__const_udelay(nsecs * 0x5UL); /* 2**32 / 1000000000 (rounded up) */
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}
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EXPORT_SYMBOL(__ndelay);
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