linux-kernel - [rt-patch 4/3] arm,KVM: Move phys_timer handling to hard irq context

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Date:   Thu, 02 Aug 2018 08:56:20 +0200
From:   Mike Galbraith <efault@....de>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [rt-patch 4/3] arm,KVM: Move phys_timer handling to hard irq context

(arm-land adventures 1/3 take2 will have to wait, my cup runeth over) 

v4.14..v4.15 timer handling changes including calling kvm_timer_vcpu_load()
during kvm_preempt_ops.sched_in and taking vgic_dist.lpi_list_lock in the
timer interrupt handler required locks for which locking rules/context had
been changed be converted to raw_spinlock_t...

Quoting virt/kvm/arm/vgic/vgic.c:
 * Locking order is always:
 * kvm->lock (mutex)
 *   its->cmd_lock (mutex)
 *     its->its_lock (mutex)
 *       vgic_cpu->ap_list_lock         must be taken with IRQs disabled
 *         kvm->lpi_list_lock           must be taken with IRQs disabled
 *           vgic_irq->irq_lock         must be taken with IRQs disabled
 *
 * As the ap_list_lock might be taken from the timer interrupt handler,
 * we have to disable IRQs before taking this lock and everything lower
 * than it.

...and fixed the obvious bricking consequence of those changes for RT,
but left an RT specific kvm unit test timer failure in its wake.  Handling
phys_timer in hard interrupt context as expected cures that failure.

Pre:
PASS selftest-setup (2 tests)
PASS selftest-vectors-kernel (2 tests)
PASS selftest-vectors-user (2 tests)
PASS selftest-smp (65 tests)
PASS pci-test (1 tests)
PASS pmu (3 tests)
PASS gicv2-ipi (3 tests)
PASS gicv3-ipi (3 tests)
PASS gicv2-active (1 tests)
PASS gicv3-active (1 tests)
PASS psci (4 tests)
FAIL timer (8 tests, 1 unexpected failures)

Post:
PASS selftest-setup (2 tests)
PASS selftest-vectors-kernel (2 tests)
PASS selftest-vectors-user (2 tests)
PASS selftest-smp (65 tests)
PASS pci-test (1 tests)
PASS pmu (3 tests)
PASS gicv2-ipi (3 tests)
PASS gicv3-ipi (3 tests)
PASS gicv2-active (1 tests)
PASS gicv3-active (1 tests)
PASS psci (4 tests)
PASS timer (8 tests)

Signed-off-by: Mike Galbraith <efault@....de>
---
 virt/kvm/arm/arch_timer.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/virt/kvm/arm/arch_timer.c
+++ b/virt/kvm/arm/arch_timer.c
@@ -634,7 +634,7 @@ void kvm_timer_vcpu_init(struct kvm_vcpu
 	hrtimer_init(&timer->bg_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
 	timer->bg_timer.function = kvm_bg_timer_expire;

-	hrtimer_init(&timer->phys_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+	hrtimer_init(&timer->phys_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
 	timer->phys_timer.function = kvm_phys_timer_expire;

 	vtimer->irq.irq = default_vtimer_irq.irq;