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

Avi Kivity
2010-08-24T09:46:56Z

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@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.
>>
> We will not. IRQs are disabled here. native_safe_halt() enables them.

Ok.

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