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Subject[PATCH RT 06/20] kvm, rt: change async pagefault code locking for PREEMPT_RT
4.1.27-rt31-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Rik van Riel <riel@redhat.com>

The async pagefault wake code can run from the idle task in exception
context, so everything here needs to be made non-preemptible.

Conversion to a simple wait queue and raw spinlock does the trick.

Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
arch/x86/kernel/kvm.c | 37 +++++++++++++++++++------------------
1 file changed, 19 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 9435620062df..ba97b5b45879 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -36,6 +36,7 @@
#include <linux/kprobes.h>
#include <linux/debugfs.h>
#include <linux/nmi.h>
+#include <linux/wait-simple.h>
#include <asm/timer.h>
#include <asm/cpu.h>
#include <asm/traps.h>
@@ -91,14 +92,14 @@ static void kvm_io_delay(void)

struct kvm_task_sleep_node {
struct hlist_node link;
- wait_queue_head_t wq;
+ struct swait_head wq;
u32 token;
int cpu;
bool halted;
};

static struct kvm_task_sleep_head {
- spinlock_t lock;
+ raw_spinlock_t lock;
struct hlist_head list;
} async_pf_sleepers[KVM_TASK_SLEEP_HASHSIZE];

@@ -122,17 +123,17 @@ void kvm_async_pf_task_wait(u32 token)
u32 key = hash_32(token, KVM_TASK_SLEEP_HASHBITS);
struct kvm_task_sleep_head *b = &async_pf_sleepers[key];
struct kvm_task_sleep_node n, *e;
- DEFINE_WAIT(wait);
+ DEFINE_SWAITER(wait);

rcu_irq_enter();

- spin_lock(&b->lock);
+ raw_spin_lock(&b->lock);
e = _find_apf_task(b, token);
if (e) {
/* dummy entry exist -> wake up was delivered ahead of PF */
hlist_del(&e->link);
kfree(e);
- spin_unlock(&b->lock);
+ raw_spin_unlock(&b->lock);

rcu_irq_exit();
return;
@@ -141,13 +142,13 @@ void kvm_async_pf_task_wait(u32 token)
n.token = token;
n.cpu = smp_processor_id();
n.halted = is_idle_task(current) || preempt_count() > 1;
- init_waitqueue_head(&n.wq);
+ init_swait_head(&n.wq);
hlist_add_head(&n.link, &b->list);
- spin_unlock(&b->lock);
+ raw_spin_unlock(&b->lock);

for (;;) {
if (!n.halted)
- prepare_to_wait(&n.wq, &wait, TASK_UNINTERRUPTIBLE);
+ swait_prepare(&n.wq, &wait, TASK_UNINTERRUPTIBLE);
if (hlist_unhashed(&n.link))
break;

@@ -166,7 +167,7 @@ void kvm_async_pf_task_wait(u32 token)
}
}
if (!n.halted)
- finish_wait(&n.wq, &wait);
+ swait_finish(&n.wq, &wait);

rcu_irq_exit();
return;
@@ -178,8 +179,8 @@ static void apf_task_wake_one(struct kvm_task_sleep_node *n)
hlist_del_init(&n->link);
if (n->halted)
smp_send_reschedule(n->cpu);
- else if (waitqueue_active(&n->wq))
- wake_up(&n->wq);
+ else if (swaitqueue_active(&n->wq))
+ swait_wake(&n->wq);
}

static void apf_task_wake_all(void)
@@ -189,14 +190,14 @@ static void apf_task_wake_all(void)
for (i = 0; i < KVM_TASK_SLEEP_HASHSIZE; i++) {
struct hlist_node *p, *next;
struct kvm_task_sleep_head *b = &async_pf_sleepers[i];
- spin_lock(&b->lock);
+ raw_spin_lock(&b->lock);
hlist_for_each_safe(p, next, &b->list) {
struct kvm_task_sleep_node *n =
hlist_entry(p, typeof(*n), link);
if (n->cpu == smp_processor_id())
apf_task_wake_one(n);
}
- spin_unlock(&b->lock);
+ raw_spin_unlock(&b->lock);
}
}

@@ -212,7 +213,7 @@ void kvm_async_pf_task_wake(u32 token)
}

again:
- spin_lock(&b->lock);
+ raw_spin_lock(&b->lock);
n = _find_apf_task(b, token);
if (!n) {
/*
@@ -225,17 +226,17 @@ again:
* Allocation failed! Busy wait while other cpu
* handles async PF.
*/
- spin_unlock(&b->lock);
+ raw_spin_unlock(&b->lock);
cpu_relax();
goto again;
}
n->token = token;
n->cpu = smp_processor_id();
- init_waitqueue_head(&n->wq);
+ init_swait_head(&n->wq);
hlist_add_head(&n->link, &b->list);
} else
apf_task_wake_one(n);
- spin_unlock(&b->lock);
+ raw_spin_unlock(&b->lock);
return;
}
EXPORT_SYMBOL_GPL(kvm_async_pf_task_wake);
@@ -486,7 +487,7 @@ void __init kvm_guest_init(void)
paravirt_ops_setup();
register_reboot_notifier(&kvm_pv_reboot_nb);
for (i = 0; i < KVM_TASK_SLEEP_HASHSIZE; i++)
- spin_lock_init(&async_pf_sleepers[i].lock);
+ raw_spin_lock_init(&async_pf_sleepers[i].lock);
if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF))
x86_init.irqs.trap_init = kvm_apf_trap_init;

--
2.8.1

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