On 11/01/2009 01:56 PM, Gleb Natapov wrote:
Asynchronous page fault notifies vcpu that page it is trying to access
is swapped out by a host. In response guest puts a task that caused the
fault to sleep until page is swapped in again. When missing page is
brought back into the memory guest is notified and task resumes execution.
diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
index 90708b7..61e2aa3 100644
--- a/arch/x86/include/asm/kvm_para.h
+++ b/arch/x86/include/asm/kvm_para.h
@@ -52,6 +52,9 @@ struct kvm_mmu_op_release_pt {
#define KVM_PV_SHM_FEATURES_ASYNC_PF (1<< 0)
+#define KVM_PV_REASON_PAGE_NP 1
+#define KVM_PV_REASON_PAGE_READY 2
_NOT_PRESENT would improve readability.
+static void apf_task_wait(struct task_struct *tsk, u64 token)
{
+ u64 key = hash_64(token, KVM_TASK_SLEEP_HASHBITS);
+ struct kvm_task_sleep_head *b =&async_pf_sleepers[key];
+ struct kvm_task_sleep_node n, *e;
+ DEFINE_WAIT(wait);
+
+ spin_lock(&b->lock);
+ e = _find_apf_task(b, token);
+ if (e) {
+ /* dummy entry exist -> wake up was delivered ahead of PF */
+ hlist_del(&e->link);
+ kfree(e);
+ spin_unlock(&b->lock);
+ return;
+ }
+
+ n.token = token;
+ 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 (hlist_unhashed(&n.link))
+ break;
Don't you need locking here? At least for the implied memory barriers.
+ schedule();
+ }
+ finish_wait(&n.wq,&wait);
+
+ return;
+}
+
+static void apf_task_wake(u64 token)
+{
+ u64 key = hash_64(token, KVM_TASK_SLEEP_HASHBITS);
+ struct kvm_task_sleep_head *b =&async_pf_sleepers[key];
+ struct kvm_task_sleep_node *n;
+
+ spin_lock(&b->lock);
+ n = _find_apf_task(b, token);
+ if (!n) {
+ /* PF was not yet handled. Add dummy entry for the token */
+ n = kmalloc(sizeof(*n), GFP_ATOMIC);
+ if (!n) {
+ printk(KERN_EMERG"async PF can't allocate memory\n");
Worrying. We could have an emergency pool of one node per cpu, and
disable apf if we use it until it's returned. But that's a lot of
complexity for an edge case, so a simpler solution would be welcome.
+int kvm_handle_pf(struct pt_regs *regs, unsigned long error_code)
+{
+ u64 reason, token;
struct kvm_vcpu_pv_shm *pv_shm =
per_cpu(kvm_vcpu_pv_shm, smp_processor_id());
if (!pv_shm)
- return;
+ return 0;
+
+ reason = pv_shm->reason;
+ pv_shm->reason = 0;
+
+ token = pv_shm->param;
+
+ switch (reason) {
+ default:
+ return 0;
+ case KVM_PV_REASON_PAGE_NP:
+ /* real page is missing. */
+ apf_task_wait(current, token);
+ break;
+ case KVM_PV_REASON_PAGE_READY:
+ apf_task_wake(token);
+ break;
+ }
Ah, reason is not a bitmask but an enumerator. __u32 is more friendly
to i386 in that case.
Much of the code here is arch independent and would work well on non-x86
kvm ports. But we can always lay the burden of moving it on the non-x86
maintainers.
--
error compiling committee.c: too many arguments to function
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