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KVM paravirt: Handle async PF in non preemptable context

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If async page fault is received by idle task or when preemp_count is
not zero guest cannot reschedule, so do sti; hlt and wait for page to be
ready. vcpu can still process interrupts while it waits for the page to
be ready.

Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Gleb Natapov 2010-10-14 11:22:54 +02:00 committed by Avi Kivity
parent 7c90705bf2
commit 6c047cd982
1 changed files with 34 additions and 6 deletions
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40
arch/x86/kernel/kvm.c
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@ -37,6 +37,7 @@
#include <asm/cpu.h>
#include <asm/traps.h>
#include <asm/desc.h>
#include <asm/tlbflush.h>
#define MMU_QUEUE_SIZE 1024
@ -78,6 +79,8 @@ struct kvm_task_sleep_node {
wait_queue_head_t wq;
u32 token;
int cpu;
bool halted;
struct mm_struct *mm;
};
static struct kvm_task_sleep_head {
@ -106,6 +109,11 @@ void kvm_async_pf_task_wait(u32 token)
struct kvm_task_sleep_head *b = &async_pf_sleepers[key];
struct kvm_task_sleep_node n, *e;
DEFINE_WAIT(wait);
int cpu, idle;
cpu = get_cpu();
idle = idle_cpu(cpu);
put_cpu();
spin_lock(&b->lock);
e = _find_apf_task(b, token);
@ -119,19 +127,33 @@ void kvm_async_pf_task_wait(u32 token)
n.token = token;
n.cpu = smp_processor_id();
n.mm = current->active_mm;
n.halted = idle || preempt_count() > 1;
atomic_inc(&n.mm->mm_count);
init_waitqueue_head(&n.wq);
hlist_add_head(&n.link, &b->list);
spin_unlock(&b->lock);
for (;;) {
prepare_to_wait(&n.wq, &wait, TASK_UNINTERRUPTIBLE);
if (!n.halted)
prepare_to_wait(&n.wq, &wait, TASK_UNINTERRUPTIBLE);
if (hlist_unhashed(&n.link))
break;
local_irq_enable();
schedule();
local_irq_disable();
if (!n.halted) {
local_irq_enable();
schedule();
local_irq_disable();
} else {
/*
* We cannot reschedule. So halt.
*/
native_safe_halt();
local_irq_disable();
}
}
finish_wait(&n.wq, &wait);
if (!n.halted)
finish_wait(&n.wq, &wait);
return;
}
@ -140,7 +162,12 @@ EXPORT_SYMBOL_GPL(kvm_async_pf_task_wait);
static void apf_task_wake_one(struct kvm_task_sleep_node *n)
{
hlist_del_init(&n->link);
if (waitqueue_active(&n->wq))
if (!n->mm)
return;
mmdrop(n->mm);
if (n->halted)
smp_send_reschedule(n->cpu);
else if (waitqueue_active(&n->wq))
wake_up(&n->wq);
}
@ -193,6 +220,7 @@ again:
}
n->token = token;
n->cpu = smp_processor_id();
n->mm = NULL;
init_waitqueue_head(&n->wq);
hlist_add_head(&n->link, &b->list);
} else