Re: [PATCH v5 10/12] Handle async PF in non preemptable context

Avi Kivity
2010-08-24T09:31:27Z

On 07/19/2010 06:31 PM, Gleb Natapov wrote:
> 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>
> ---
> arch/x86/kernel/kvm.c | 36 ++++++++++++++++++++++++++++++++----
> 1 files changed, 32 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index a6db92e..914b0fc 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -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
>
> @@ -68,6 +69,8 @@ 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 {
> @@ -96,6 +99,11 @@ static void apf_task_wait(struct task_struct *tsk, 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);
> @@ -109,17 +117,31 @@ static void apf_task_wait(struct task_struct *tsk, 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;
> - schedule();
> +
> + if (!n.halted) {
> + schedule();
> + } else {
> + /*
> + * We cannot reschedule. So halt.
> + */

If we get the wakeup here, we'll halt and never wake up again.

> + native_safe_halt();
> + local_irq_disable();

So we need a local_irq_disable() before the hlish_unhashed() check.

> + }
> }
> - finish_wait(&n.wq,&wait);
> + if (!n.halted)
> + finish_wait(&n.wq,&wait);
>
> return;
> }
> @@ -127,7 +149,12 @@ static void apf_task_wait(struct task_struct *tsk, u32 token)
> 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);
> }
>
> @@ -157,6 +184,7 @@ 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

--
error compiling committee.c: too many arguments to function