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

Gleb Natapov
2010-07-19T15:31:33Z

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.
+ */
+ native_safe_halt();
+ local_irq_disable();
+ }
}
- 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
--
1.7.1