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

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Date:	Tue, 24 Aug 2010 12:46:27 +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 08/24/2010 12:36 PM, Gleb Natapov wrote:
> On Tue, Aug 24, 2010 at 12:30:25PM +0300, Avi Kivity wrote:
>>   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.
>>
> We will not. IRQs are disabled here. native_safe_halt() enables them.

Ok.

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

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