KVM: selftests: Add EVTCHNOP_send slow path test to xen_shinfo_test

When kvm_xen_evtchn_send() takes the slow path because the shinfo GPC
needs to be revalidated, it used to violate the SRCU vs. kvm->lock
locking rules and potentially cause a deadlock.

Now that lockdep is learning to catch such things, make sure that code
path is exercised by the selftest.

Link: https://lore.kernel.org/all/20230113124606.10221-2-dwmw2@infradead.org
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230204024151.1373296-5-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: dwmw2

tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c

@@ -26,6 +26,9 @@
 #define DUMMY_REGION_GPA	(SHINFO_REGION_GPA + (3 * PAGE_SIZE))
 #define DUMMY_REGION_SLOT	11
 
+#define DUMMY_REGION_GPA_2	(SHINFO_REGION_GPA + (4 * PAGE_SIZE))
+#define DUMMY_REGION_SLOT_2	12
+
 #define SHINFO_ADDR	(SHINFO_REGION_GPA)
 #define VCPU_INFO_ADDR	(SHINFO_REGION_GPA + 0x40)
 #define PVTIME_ADDR	(SHINFO_REGION_GPA + PAGE_SIZE)
@@ -54,6 +57,7 @@ enum {
 	TEST_EVTCHN_SLOWPATH,
 	TEST_EVTCHN_SEND_IOCTL,
 	TEST_EVTCHN_HCALL,
+	TEST_EVTCHN_HCALL_SLOWPATH,
 	TEST_EVTCHN_HCALL_EVENTFD,
 	TEST_TIMER_SETUP,
 	TEST_TIMER_WAIT,
@@ -260,6 +264,16 @@ static void guest_code(void)
 
 	guest_wait_for_irq();
 
+	GUEST_SYNC(TEST_EVTCHN_HCALL_SLOWPATH);
+
+	/*
+	 * Same again, but this time the host has messed with memslots so it
+	 * should take the slow path in kvm_xen_set_evtchn().
+	 */
+	xen_hypercall(__HYPERVISOR_event_channel_op, EVTCHNOP_send, &s);
+
+	guest_wait_for_irq();
+
 	GUEST_SYNC(TEST_EVTCHN_HCALL_EVENTFD);
 
 	/* Deliver "outbound" event channel to an eventfd which
@@ -753,6 +767,19 @@ int main(int argc, char *argv[])
 				alarm(1);
 				break;
 
+			case TEST_EVTCHN_HCALL_SLOWPATH:
+				TEST_ASSERT(!evtchn_irq_expected,
+					    "Expected event channel IRQ but it didn't happen");
+				shinfo->evtchn_pending[0] = 0;
+
+				if (verbose)
+					printf("Testing guest EVTCHNOP_send direct to evtchn after memslot change\n");
+				vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS,
+							    DUMMY_REGION_GPA_2, DUMMY_REGION_SLOT_2, 1, 0);
+				evtchn_irq_expected = true;
+				alarm(1);
+				break;
+
 			case TEST_EVTCHN_HCALL_EVENTFD:
 				TEST_ASSERT(!evtchn_irq_expected,
 					    "Expected event channel IRQ but it didn't happen");