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Commit 6c047cd9 authored by Gleb Natapov's avatar Gleb Natapov Committed by Avi Kivity
Browse files

KVM paravirt: Handle async PF in non preemptable context 



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: default avatarRik van Riel <riel@redhat.com>
Signed-off-by: default avatarGleb Natapov <gleb@redhat.com>
Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
parent 7c90705b

arch/x86/kernel/kvm.c

+34 −6
Original line number Diff line number Diff line
@@ -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
@@ -78,6 +79,8 @@ 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 {
@@ -106,6 +109,11 @@ void kvm_async_pf_task_wait(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);
@@ -119,18 +127,32 @@ void kvm_async_pf_task_wait(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 (;;) {

		if (!n.halted)

			prepare_to_wait(&n.wq, &wait, TASK_UNINTERRUPTIBLE);

		if (hlist_unhashed(&n.link))

			break;



		if (!n.halted) {

			local_irq_enable();

			schedule();

			local_irq_disable();

		} else {

			/*

			 * We cannot reschedule. So halt.

			 */

			native_safe_halt();

			local_irq_disable();

		}

	}

	if (!n.halted)

		finish_wait(&n.wq, &wait);



	return;
@@ -140,7 +162,12 @@ EXPORT_SYMBOL_GPL(kvm_async_pf_task_wait); 
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);

}
@@ -193,6 +220,7 @@ void kvm_async_pf_task_wake(u32 token) 
		}

		n->token = token;

		n->cpu = smp_processor_id();

		n->mm = NULL;

		init_waitqueue_head(&n->wq);

		hlist_add_head(&n->link, &b->list);

	} else