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

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 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@xxxxxxxxxx>
Signed-off-by: Gleb Natapov<gleb@xxxxxxxxxx>
---
  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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