KVM: Halt vcpu if page it tries to access is swapped out

If a guest accesses swapped out memory do not swap it in from vcpu thread
context. Schedule work to do swapping and put vcpu into halted state
instead.

Interrupts will still be delivered to the guest and if interrupt will
cause reschedule guest will continue to run another task.

[avi: remove call to get_user_pages_noio(), nacked by Linus; this
      makes everything synchrnous again]

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

include/trace/events/kvm.h

@@ -185,6 +185,96 @@ TRACE_EVENT(kvm_age_page,
 		  __entry->referenced ? "YOUNG" : "OLD")
 );
 
+#ifdef CONFIG_KVM_ASYNC_PF
+TRACE_EVENT(
+	kvm_try_async_get_page,
+	TP_PROTO(bool async, u64 pfn),
+	TP_ARGS(async, pfn),
+
+	TP_STRUCT__entry(
+		__field(__u64, pfn)
+		),
+
+	TP_fast_assign(
+		__entry->pfn = (!async) ? pfn : (u64)-1;
+		),
+
+	TP_printk("pfn %#llx", __entry->pfn)
+);
+
+TRACE_EVENT(
+	kvm_async_pf_not_present,
+	TP_PROTO(u64 gva),
+	TP_ARGS(gva),
+
+	TP_STRUCT__entry(
+		__field(__u64, gva)
+		),
+
+	TP_fast_assign(
+		__entry->gva = gva;
+		),
+
+	TP_printk("gva %#llx not present", __entry->gva)
+);
+
+TRACE_EVENT(
+	kvm_async_pf_ready,
+	TP_PROTO(u64 gva),
+	TP_ARGS(gva),
+
+	TP_STRUCT__entry(
+		__field(__u64, gva)
+		),
+
+	TP_fast_assign(
+		__entry->gva = gva;
+		),
+
+	TP_printk("gva %#llx ready", __entry->gva)
+);
+
+TRACE_EVENT(
+	kvm_async_pf_completed,
+	TP_PROTO(unsigned long address, struct page *page, u64 gva),
+	TP_ARGS(address, page, gva),
+
+	TP_STRUCT__entry(
+		__field(unsigned long, address)
+		__field(pfn_t, pfn)
+		__field(u64, gva)
+		),
+
+	TP_fast_assign(
+		__entry->address = address;
+		__entry->pfn = page ? page_to_pfn(page) : 0;
+		__entry->gva = gva;
+		),
+
+	TP_printk("gva %#llx address %#lx pfn %#llx",  __entry->gva,
+		  __entry->address, __entry->pfn)
+);
+
+TRACE_EVENT(
+	kvm_async_pf_doublefault,
+	TP_PROTO(u64 gva, u64 gfn),
+	TP_ARGS(gva, gfn),
+
+	TP_STRUCT__entry(
+		__field(u64, gva)
+		__field(u64, gfn)
+		),
+
+	TP_fast_assign(
+		__entry->gva = gva;
+		__entry->gfn = gfn;
+		),
+
+	TP_printk("gva = %#llx, gfn = %#llx", __entry->gva, __entry->gfn)
+);
+
+#endif
+
 #endif /* _TRACE_KVM_MAIN_H */
 
 /* This part must be outside protection */