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

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Date:	Tue, 24 Aug 2010 12:30:25 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	kvm@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, mingo@...e.hu,
	a.p.zijlstra@...llo.nl, tglx@...utronix.de, hpa@...or.com,
	riel@...hat.com, cl@...ux-foundation.org, mtosatti@...hat.com
Subject: Re: [PATCH v5 10/12] Handle async PF in non preemptable context

  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@...hat.com>
> Signed-off-by: Gleb Natapov<gleb@...hat.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

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