KVM: Add async communication helper functions

Some KVM tests need to communicate with VM controller program
without stopping guest execution. Add guest helper functions
for sending asynchronous guest signal to host and waiting for host
to acknowledge the signal. Add host helper functions for waiting
for guest signal and acknowledging it.

Test programs using these functions must have at least two host threads.

Signed-off-by: Martin Doucha <mdoucha@suse.cz>
Reviewed-by: Petr Vorel <pvorel@suse.cz>
Reviewed-by: Cyril Hrubis <chrubis@suse.cz>

Author: mdoucha

testcases/kernel/kvm/include/kvm_common.h

@@ -10,6 +10,14 @@
 
 #define KVM_TNONE	-1	/* "No result" status value */
 
+/*
+ * Result value for asynchronous notifications between guest and host.
+ * Do not use this value directly. Call tst_signal_host() or tst_wait_host()
+ * in guest code. The notification must be handled by another host thread
+ * and then the result value must be reset to KVM_TNONE.
+ */
+#define KVM_TSYNC	0xfe
+
 /*
  * Result value indicating end of test. If the test program exits using
  * the HLT instruction with any valid result value other than KVM_TEXIT or

testcases/kernel/kvm/include/kvm_guest.h

@@ -64,6 +64,20 @@ void tst_brk_(const char *file, const int lineno, int result,
 	const char *message) __attribute__((noreturn));
 #define tst_brk(result, msg) tst_brk_(__FILE__, __LINE__, (result), (msg))
 
+/*
+ * Send asynchronous notification to host without stopping VM execution and
+ * return immediately. The notification must be handled by another host thread.
+ * The data argument will be passed to host in test_result->file_addr and
+ * can be used to send additional data both ways.
+ */
+void tst_signal_host(void *data);
+
+/*
+ * Call tst_signal_host(data) and wait for host to call
+ * tst_kvm_clear_guest_signal().
+ */
+void tst_wait_host(void *data);
+
 void *tst_heap_alloc_aligned(size_t size, size_t align);
 void *tst_heap_alloc(size_t size);
 

testcases/kernel/kvm/include/kvm_host.h

@@ -136,4 +136,18 @@ int tst_kvm_run_instance(struct tst_kvm_instance *inst, int exp_errno);
  */
 void tst_kvm_destroy_instance(struct tst_kvm_instance *inst);
 
+/*
+ * Wait for given VM to call tst_signal_host() or tst_wait_host(). Timeout
+ * value is in milliseconds. Zero means no wait, negative value means wait
+ * forever. Returns 0 if signal was received, KVM_TEXIT if the VM exited
+ * without sending a signal, or -1 if timeout was reached.
+ */
+int tst_kvm_wait_guest(struct tst_kvm_instance *inst, int timeout_ms);
+
+/*
+ * Clear VM signal sent by tst_signal_host(). If the VM is waiting
+ * in tst_wait_host(), this function will signal the VM to resume execution.
+ */
+void tst_kvm_clear_guest_signal(struct tst_kvm_instance *inst);
+
 #endif /* KVM_HOST_H_ */

testcases/kernel/kvm/lib_guest.c

@@ -155,6 +155,22 @@ void tst_brk_(const char *file, const int lineno, int result,
 	kvm_exit();
 }
 
+void tst_signal_host(void *data)
+{
+	test_result->file_addr = (uintptr_t)data;
+	test_result->result = KVM_TSYNC;
+}
+
+void tst_wait_host(void *data)
+{
+	volatile int32_t *vres = &test_result->result;
+
+	tst_signal_host(data);
+
+	while (*vres != KVM_TNONE)
+		;
+}
+
 void tst_handle_interrupt(struct kvm_interrupt_frame *ifrm, long vector,
 	unsigned long errcode)
 {

testcases/kernel/kvm/lib_host.c

@@ -10,6 +10,8 @@
 
 #define TST_NO_DEFAULT_MAIN
 #include "tst_test.h"
+#include "tst_clocks.h"
+#include "tst_timer.h"
 #include "kvm_host.h"
 
 static struct tst_kvm_instance test_vm = { .vm_fd = -1 };
@@ -288,6 +290,37 @@ void tst_kvm_destroy_instance(struct tst_kvm_instance *inst)
 	memset(inst->ram, 0, sizeof(inst->ram));
 }
 
+int tst_kvm_wait_guest(struct tst_kvm_instance *inst, int timeout_ms)
+{
+	volatile struct tst_kvm_result *result = inst->result;
+	int32_t res;
+	struct timespec start, now;
+
+	if (timeout_ms >= 0)
+		tst_clock_gettime(CLOCK_MONOTONIC, &start);
+
+	while ((res = result->result) != KVM_TSYNC) {
+		if (res == KVM_TEXIT)
+			return res;
+
+		if (timeout_ms >= 0) {
+			tst_clock_gettime(CLOCK_MONOTONIC, &now);
+
+			if (tst_timespec_diff_ms(now, start) >= timeout_ms)
+				return -1;
+		}
+
+		usleep(1000);
+	}
+
+	return 0;
+}
+
+void tst_kvm_clear_guest_signal(struct tst_kvm_instance *inst)
+{
+	inst->result->result = KVM_TNONE;
+}
+
 void tst_kvm_setup(void)
 {