[PATCH v2 3/8] kvm tools: Allow pausing guests

[Sasha Levin <levinsasha928@gmail.com>]

Allow pausing and unpausing guests running on the host.
Pausing a guest means that none of the VCPU threads are running
KVM_RUN until they are unpaused.

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
---
 tools/kvm/include/kvm/kvm-cpu.h |    1 +
 tools/kvm/include/kvm/kvm.h     |    4 +++
 tools/kvm/kvm-cpu.c             |   20 +++++++++++---
 tools/kvm/kvm-run.c             |    4 +-
 tools/kvm/kvm.c                 |   54 +++++++++++++++++++++++++++++++++++++++
 5 files changed, 76 insertions(+), 7 deletions(-)

diff --git a/tools/kvm/include/kvm/kvm-cpu.h b/tools/kvm/include/kvm/kvm-cpu.h
index b2b6fce..4d99246 100644
--- a/tools/kvm/include/kvm/kvm-cpu.h
+++ b/tools/kvm/include/kvm/kvm-cpu.h
@@ -23,6 +23,7 @@ struct kvm_cpu {
 	struct kvm_msrs		*msrs;		/* dynamically allocated */
 
 	u8			is_running;
+	u8			paused;
 };
 
 struct kvm_cpu *kvm_cpu__init(struct kvm *kvm, unsigned long cpu_id);
diff --git a/tools/kvm/include/kvm/kvm.h b/tools/kvm/include/kvm/kvm.h
index 6a17362..d22a849 100644
--- a/tools/kvm/include/kvm/kvm.h
+++ b/tools/kvm/include/kvm/kvm.h
@@ -12,6 +12,7 @@
 #define KVM_32BIT_GAP_START	((1ULL << 32) - KVM_32BIT_GAP_SIZE)
 
 #define SIGKVMEXIT		(SIGRTMIN + 0)
+#define SIGKVMPAUSE		(SIGRTMIN + 1)
 
 struct kvm {
 	int			sys_fd;		/* For system ioctls(), i.e. /dev/kvm */
@@ -50,6 +51,9 @@ bool kvm__emulate_io(struct kvm *kvm, u16 port, void *data, int direction, int s
 bool kvm__emulate_mmio(struct kvm *kvm, u64 phys_addr, u8 *data, u32 len, u8 is_write);
 bool kvm__register_mmio(u64 phys_addr, u64 phys_addr_len, void (*kvm_mmio_callback_fn)(u64 addr, u8 *data, u32 len, u8 is_write));
 bool kvm__deregister_mmio(u64 phys_addr);
+void kvm__pause(void);
+void kvm__continue(void);
+void kvm__notify_paused(void);
 
 /*
  * Debugging
diff --git a/tools/kvm/kvm-cpu.c b/tools/kvm/kvm-cpu.c
index de0591f..be0528b 100644
--- a/tools/kvm/kvm-cpu.c
+++ b/tools/kvm/kvm-cpu.c
@@ -383,11 +383,15 @@ void kvm_cpu__run(struct kvm_cpu *vcpu)
 		die_perror("KVM_RUN failed");
 }
 
-static void kvm_cpu_exit_handler(int signum)
+static void kvm_cpu_signal_handler(int signum)
 {
-	if (current_kvm_cpu->is_running) {
-		current_kvm_cpu->is_running = false;
-		pthread_kill(pthread_self(), SIGKVMEXIT);
+	if (signum == SIGKVMEXIT) {
+		if (current_kvm_cpu->is_running) {
+			current_kvm_cpu->is_running = false;
+			pthread_kill(pthread_self(), SIGKVMEXIT);
+		}
+	} else if (signum == SIGKVMPAUSE) {
+		current_kvm_cpu->paused = 1;
 	}
 }
 
@@ -400,12 +404,18 @@ int kvm_cpu__start(struct kvm_cpu *cpu)
 
 	pthread_sigmask(SIG_BLOCK, &sigset, NULL);
 
-	signal(SIGKVMEXIT, kvm_cpu_exit_handler);
+	signal(SIGKVMEXIT, kvm_cpu_signal_handler);
+	signal(SIGKVMPAUSE, kvm_cpu_signal_handler);
 
 	kvm_cpu__setup_cpuid(cpu);
 	kvm_cpu__reset_vcpu(cpu);
 
 	for (;;) {
+		if (cpu->paused) {
+			kvm__notify_paused();
+			cpu->paused = 0;
+		}
+
 		kvm_cpu__run(cpu);
 
 		switch (cpu->kvm_run->exit_reason) {
diff --git a/tools/kvm/kvm-run.c b/tools/kvm/kvm-run.c
index 48b8e70..761ac0d 100644
--- a/tools/kvm/kvm-run.c
+++ b/tools/kvm/kvm-run.c
@@ -47,8 +47,8 @@
 #define MIN_RAM_SIZE_MB		(64ULL)
 #define MIN_RAM_SIZE_BYTE	(MIN_RAM_SIZE_MB << MB_SHIFT)
 
-static struct kvm *kvm;
-static struct kvm_cpu *kvm_cpus[KVM_NR_CPUS];
+struct kvm *kvm;
+struct kvm_cpu *kvm_cpus[KVM_NR_CPUS];
 __thread struct kvm_cpu *current_kvm_cpu;
 
 static u64 ram_size;
diff --git a/tools/kvm/kvm.c b/tools/kvm/kvm.c
index 1d756e0..54e3203 100644
--- a/tools/kvm/kvm.c
+++ b/tools/kvm/kvm.c
@@ -6,6 +6,8 @@
 #include "kvm/interrupt.h"
 #include "kvm/mptable.h"
 #include "kvm/util.h"
+#include "kvm/mutex.h"
+#include "kvm/kvm-cpu.h"
 
 #include <linux/kvm.h>
 
@@ -25,6 +27,7 @@
 #include <stdio.h>
 #include <fcntl.h>
 #include <time.h>
+#include <sys/eventfd.h>
 
 #define DEFINE_KVM_EXIT_REASON(reason) [reason] = #reason
 
@@ -68,6 +71,11 @@ struct {
 	{ DEFINE_KVM_EXT(KVM_CAP_EXT_CPUID) },
 };
 
+extern struct kvm *kvm;
+extern struct kvm_cpu *kvm_cpus[KVM_NR_CPUS];
+static int pause_event;
+static DEFINE_MUTEX(pause_lock);
+
 static bool kvm__supports_extension(struct kvm *kvm, unsigned int extension)
 {
 	int ret;
@@ -575,3 +583,49 @@ void kvm__dump_mem(struct kvm *kvm, unsigned long addr, unsigned long size)
 				  p[n + 4], p[n + 5], p[n + 6], p[n + 7]);
 	}
 }
+
+void kvm__pause(void)
+{
+	int i, paused_vcpus = 0;
+
+	/* Check if the guest is running */
+	if (!kvm_cpus[0] || kvm_cpus[0]->thread == 0)
+		return;
+
+	mutex_lock(&pause_lock);
+
+	pause_event = eventfd(0, 0);
+	if (pause_event < 0)
+		die("Failed creating pause notification event");
+	for (i = 0; i < kvm->nrcpus; i++)
+		pthread_kill(kvm_cpus[i]->thread, SIGKVMPAUSE);
+
+	while (paused_vcpus < kvm->nrcpus) {
+		u64 cur_read;
+
+		if (read(pause_event, &cur_read, sizeof(cur_read)) < 0)
+			die("Failed reading pause event");
+		paused_vcpus += cur_read;
+	}
+	close(pause_event);
+}
+
+void kvm__continue(void)
+{
+	/* Check if the guest is running */
+	if (!kvm_cpus[0] || kvm_cpus[0]->thread == 0)
+		return;
+
+	mutex_unlock(&pause_lock);
+}
+
+void kvm__notify_paused(void)
+{
+	u64 p = 1;
+
+	if (write(pause_event, &p, sizeof(p)) < 0)
+		die("Failed notifying of paused VCPU.");
+
+	mutex_lock(&pause_lock);
+	mutex_unlock(&pause_lock);
+}
-- 
1.7.5.rc3