KVM: Inject asynchronous page fault into a PV guest if page is swapped out.

Send async page fault to a PV guest if it accesses swapped out memory.
Guest will choose another task to run upon receiving the fault.

Allow async page fault injection only when guest is in user mode since
otherwise guest may be in non-sleepable context and will not be able
to reschedule.

Vcpu will be halted if guest will fault on the same page again or if
vcpu executes kernel code.

Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
index 1f59498561b2..60df9e059e69 100644
--- a/virt/kvm/async_pf.c
+++ b/virt/kvm/async_pf.c
@@ -124,7 +124,8 @@ void kvm_check_async_pf_completion(struct kvm_vcpu *vcpu)
 {
         struct kvm_async_pf *work;
 
-        if (list_empty_careful(&vcpu->async_pf.done))
+        if (list_empty_careful(&vcpu->async_pf.done) ||
+            !kvm_arch_can_inject_async_page_present(vcpu))
                 return;
 
         spin_lock(&vcpu->async_pf.lock);