[PATCH 2/2] ptrace_vm: ptrace for syscall emulation virtual machines

[PATCH 2/2] ptrace_vm: ptrace for syscall emulation virtual machines

[Renzo Davoli]

This patch adds the new PTRACE_VM_SKIPCALL and PTRACE_VM_SKIPEXIT
tags for ptrace's addr parameter.
In this way it is possible to (eventually) get rid of PTRACE_SYSEMU
PTRACE_SYSEMU_SINGLESTEP, while providing not only the same features
but a more general support for Virtual Machines.
Part#2: user-mode Linux support. 
User-mode Linux by this patch uses PTRACE_VM of the hosting operating system
and provides PTRACE_VM to its processes.
UML tests at startup which features are provided and uses PTRACE_VM or
PTRACE_SYSEMU (or nothing). PTRACE_VM and/or PTRACE_SYSEMU support can be 
disabled by command line flags.
It is possible to test this patch by running a UML inside a UML (note that with
vanilla kernel UML on UML is currently broken without the patchfix I
published a few days ago. If you apply just the patch of this message UML on 
UML works provided that the outer UML provides PTRACE_VM and the support 
for PTRACE_VM in the inner UML is not disabled, otherwise my previous patch 
is needed. Shortcut: apply my previous patch before this in any case)

renzo

Signed-off-by: Renzo Davoli <renzo@cs.unibo.it>
---
diff -Naur linux-2.6.28.2/arch/um/include/shared/kern_util.h linux-2.6.28.2-vm/arch/um/include/shared/kern_util.h
--- linux-2.6.28.2/arch/um/include/shared/kern_util.h	2009-01-25 01:42:07.000000000 +0100
+++ linux-2.6.28.2-vm/arch/um/include/shared/kern_util.h	2009-02-02 14:31:32.000000000 +0100
@@ -57,7 +57,7 @@
 extern unsigned long to_irq_stack(unsigned long *mask_out);
 extern unsigned long from_irq_stack(int nested);
 
-extern void syscall_trace(struct uml_pt_regs *regs, int entryexit);
+extern int syscall_trace(struct uml_pt_regs *regs, int entryexit);
 extern int singlestepping(void *t);
 
 extern void segv_handler(int sig, struct uml_pt_regs *regs);
diff -Naur linux-2.6.28.2/arch/um/include/shared/ptrace_user.h linux-2.6.28.2-vm/arch/um/include/shared/ptrace_user.h
--- linux-2.6.28.2/arch/um/include/shared/ptrace_user.h	2009-01-25 01:42:07.000000000 +0100
+++ linux-2.6.28.2-vm/arch/um/include/shared/ptrace_user.h	2009-02-02 14:31:32.000000000 +0100
@@ -40,9 +40,20 @@
 #define PTRACE_OLDSETOPTIONS PTRACE_SETOPTIONS
 #endif
 
+/* these constant should eventually enter in sys/ptrace.h */
+#ifndef PTRACE_SYSCALL_SKIPCALL
+#define PTRACE_SYSCALL_SKIPCALL      0x6
+#endif
+#ifndef PTRACE_SYSCALL_SKIPEXIT
+#define PTRACE_SYSCALL_SKIPEXIT      0x2
+#endif
+
 void set_using_sysemu(int value);
 int get_using_sysemu(void);
 extern int sysemu_supported;
+void set_using_sysptvm(int value);
+int get_using_sysptvm(void);
+extern int sysptvm_supported;
 
 #define SELECT_PTRACE_OPERATION(sysemu_mode, singlestep_mode) \
 	(((int[3][3] ) { \
diff -Naur linux-2.6.28.2/arch/um/kernel/process.c linux-2.6.28.2-vm/arch/um/kernel/process.c
--- linux-2.6.28.2/arch/um/kernel/process.c	2009-01-25 01:42:07.000000000 +0100
+++ linux-2.6.28.2-vm/arch/um/kernel/process.c	2009-02-02 14:31:32.000000000 +0100
@@ -322,7 +322,9 @@
 }
 
 static atomic_t using_sysemu = ATOMIC_INIT(0);
+static atomic_t using_sysptvm = ATOMIC_INIT(0);
 int sysemu_supported;
+int sysptvm_supported;
 
 void set_using_sysemu(int value)
 {
@@ -336,6 +338,16 @@
 	return atomic_read(&using_sysemu);
 }
 
+void set_using_sysptvm(int value)
+{
+	atomic_set(&using_sysptvm, value);
+}
+
+int get_using_sysptvm(void)
+{
+	return atomic_read(&using_sysptvm);
+}
+
 static int proc_read_sysemu(char *buf, char **start, off_t offset, int size,int *eof, void *data)
 {
 	if (snprintf(buf, size, "%d\n", get_using_sysemu()) < size)
@@ -358,27 +370,63 @@
 	return count;
 }
 
-int __init make_proc_sysemu(void)
+
+static int proc_read_sysptvm(char *buf, char **start, off_t offset, int size,int *eof, void *data)
 {
-	struct proc_dir_entry *ent;
-	if (!sysemu_supported)
-		return 0;
+	int sysptvm=(get_using_sysptvm() != 0);
+	if (snprintf(buf, size, "%d\n", sysptvm) < size)
+		/* No overflow */
+		*eof = 1;
 
-	ent = create_proc_entry("sysemu", 0600, NULL);
+	return strlen(buf);
+}
 
-	if (ent == NULL)
-	{
-		printk(KERN_WARNING "Failed to register /proc/sysemu\n");
-		return 0;
-	}
+static int proc_write_sysptvm(struct file *file,const char __user *buf, unsigned long count,void *data)
+{
+	char tmp[2];
+
+	if (copy_from_user(tmp, buf, 1))
+		return -EFAULT;
+
+	if (tmp[0] == '0')
+		set_using_sysptvm(0);
+	if (tmp[0] == '1')
+		set_using_sysemu(/* XXX */ 6);
+	/* We use the first char, but pretend to write everything */
+	return count;
+}
 
-	ent->read_proc  = proc_read_sysemu;
-	ent->write_proc = proc_write_sysemu;
+int __init make_proc_sysemu_or_sysptvm(void)
+{
+	struct proc_dir_entry *ent;
 
+	if (sysptvm_supported) {
+		ent = create_proc_entry("sysptvm", 0600, NULL);
+
+		if (ent == NULL)
+		{
+			printk(KERN_WARNING "Failed to register /proc/sysptvm\n");
+			return 0;
+		}
+
+		ent->read_proc  = proc_read_sysptvm;
+		ent->write_proc = proc_write_sysptvm;
+	} else if (sysemu_supported) {
+		ent = create_proc_entry("sysemu", 0600, NULL);
+
+		if (ent == NULL)
+		{
+			printk(KERN_WARNING "Failed to register /proc/sysemu\n");
+			return 0;
+		}
+
+		ent->read_proc  = proc_read_sysemu;
+		ent->write_proc = proc_write_sysemu;
+	}
 	return 0;
 }
 
-late_initcall(make_proc_sysemu);
+late_initcall(make_proc_sysemu_or_sysptvm);
 
 int singlestepping(void * t)
 {
diff -Naur linux-2.6.28.2/arch/um/kernel/ptrace.c linux-2.6.28.2-vm/arch/um/kernel/ptrace.c
--- linux-2.6.28.2/arch/um/kernel/ptrace.c	2009-01-25 01:42:07.000000000 +0100
+++ linux-2.6.28.2-vm/arch/um/kernel/ptrace.c	2009-02-02 14:31:32.000000000 +0100
@@ -64,6 +64,11 @@
 		ret = poke_user(child, addr, data);
 		break;
 
+	case PTRACE_SYSEMU:
+	case PTRACE_SYSEMU_SINGLESTEP:
+		ret=-EIO;
+		break; 
+
 	/* continue and stop at next (return from) syscall */
 	case PTRACE_SYSCALL:
 	/* restart after signal. */
@@ -76,6 +81,8 @@
 		if (request == PTRACE_SYSCALL)
 			set_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 		else clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
+		child->ptrace &= ~PT_SYSCALL_MASK;
+		child->ptrace |= (addr & PTRACE_SYSCALL_MASK) << 28;
 		child->exit_code = data;
 		wake_up_process(child);
 		ret = 0;
@@ -102,7 +109,9 @@
 		ret = -EIO;
 		if (!valid_signal(data))
 			break;
+		child->ptrace &= ~PT_SYSCALL_MASK;
 		clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
+		child->ptrace |= (addr & PTRACE_SYSCALL_MASK) << 28;
 		set_singlestepping(child, 1);
 		child->exit_code = data;
 		/* give it a chance to run. */
@@ -245,7 +254,7 @@
  * XXX Check PT_DTRACE vs TIF_SINGLESTEP for singlestepping check and
  * PT_PTRACED vs TIF_SYSCALL_TRACE for syscall tracing check
  */
-void syscall_trace(struct uml_pt_regs *regs, int entryexit)
+int syscall_trace(struct uml_pt_regs *regs, int entryexit)
 {
 	int is_singlestep = (current->ptrace & PT_DTRACE) && entryexit;
 	int tracesysgood;
@@ -267,10 +276,13 @@
 		send_sigtrap(current, regs, 0);
 
 	if (!test_thread_flag(TIF_SYSCALL_TRACE))
-		return;
+		return 0;
 
 	if (!(current->ptrace & PT_PTRACED))
-		return;
+		return 0;
+
+	if (entryexit && (current->ptrace & PT_SYSCALL_SKIPEXIT))
+		return 0;
 
 	/*
 	 * the 0x80 provides a way for the tracing parent to distinguish
@@ -291,4 +303,8 @@
 		send_sig(current->exit_code, current, 1);
 		current->exit_code = 0;
 	}
+	if (!entryexit && (current->ptrace & PT_SYSCALL_SKIPCALL))
+		return 1;
+	else
+		return 0;
 }
diff -Naur linux-2.6.28.2/arch/um/kernel/skas/syscall.c linux-2.6.28.2-vm/arch/um/kernel/skas/syscall.c
--- linux-2.6.28.2/arch/um/kernel/skas/syscall.c	2009-01-25 01:42:07.000000000 +0100
+++ linux-2.6.28.2-vm/arch/um/kernel/skas/syscall.c	2009-02-02 14:31:32.000000000 +0100
@@ -17,8 +17,9 @@
 	struct pt_regs *regs = container_of(r, struct pt_regs, regs);
 	long result;
 	int syscall;
+	int skip_call;
 
-	syscall_trace(r, 0);
+	skip_call=syscall_trace(r, 0);
 
 	/*
 	 * This should go in the declaration of syscall, but when I do that,
@@ -29,12 +30,14 @@
 	 *     gcc version 4.0.1 20050727 (Red Hat 4.0.1-5)
 	 * in case it's a compiler bug.
 	 */
-	syscall = UPT_SYSCALL_NR(r);
-	if ((syscall >= NR_syscalls) || (syscall < 0))
-		result = -ENOSYS;
-	else result = EXECUTE_SYSCALL(syscall, regs);
+	if (skip_call == 0) {
+		syscall = UPT_SYSCALL_NR(r);
+		if ((syscall >= NR_syscalls) || (syscall < 0))
+			result = -ENOSYS;
+		else result = EXECUTE_SYSCALL(syscall, regs);
 
-	REGS_SET_SYSCALL_RETURN(r->gp, result);
+		REGS_SET_SYSCALL_RETURN(r->gp, result);
+	}
 
 	syscall_trace(r, 1);
 }
diff -Naur linux-2.6.28.2/arch/um/os-Linux/skas/process.c linux-2.6.28.2-vm/arch/um/os-Linux/skas/process.c
--- linux-2.6.28.2/arch/um/os-Linux/skas/process.c	2009-01-25 01:42:07.000000000 +0100
+++ linux-2.6.28.2-vm/arch/um/os-Linux/skas/process.c	2009-02-02 14:31:32.000000000 +0100
@@ -157,7 +157,7 @@
  * (in local_using_sysemu
  */
 static void handle_trap(int pid, struct uml_pt_regs *regs,
-			int local_using_sysemu)
+			int local_using_sysptvm_or_sysemu)
 {
 	int err, status;
 
@@ -167,7 +167,7 @@
 	/* Mark this as a syscall */
 	UPT_SYSCALL_NR(regs) = PT_SYSCALL_NR(regs->gp);
 
-	if (!local_using_sysemu)
+	if (!local_using_sysptvm_or_sysemu)
 	{
 		err = ptrace(PTRACE_POKEUSR, pid, PT_SYSCALL_NR_OFFSET,
 			     __NR_getpid);
@@ -354,6 +354,7 @@
 	int err, status, op, pid = userspace_pid[0];
 	/* To prevent races if using_sysemu changes under us.*/
 	int local_using_sysemu;
+	int local_using_sysptvm;
 
 	if (getitimer(ITIMER_VIRTUAL, &timer))
 		printk(UM_KERN_ERR "Failed to get itimer, errno = %d\n", errno);
@@ -375,11 +376,12 @@
 
 		/* Now we set local_using_sysemu to be used for one loop */
 		local_using_sysemu = get_using_sysemu();
+		local_using_sysptvm = get_using_sysptvm();
 
 		op = SELECT_PTRACE_OPERATION(local_using_sysemu,
 					     singlestepping(NULL));
 
-		if (ptrace(op, pid, 0, 0)) {
+		if (ptrace(op, pid, local_using_sysptvm, 0)) {
 			printk(UM_KERN_ERR "userspace - ptrace continue "
 			       "failed, op = %d, errno = %d\n", op, errno);
 			fatal_sigsegv();
diff -Naur linux-2.6.28.2/arch/um/os-Linux/start_up.c linux-2.6.28.2-vm/arch/um/os-Linux/start_up.c
--- linux-2.6.28.2/arch/um/os-Linux/start_up.c	2009-01-25 01:42:07.000000000 +0100
+++ linux-2.6.28.2-vm/arch/um/os-Linux/start_up.c	2009-02-02 14:31:32.000000000 +0100
@@ -198,6 +198,35 @@
 "    See http://perso.wanadoo.fr/laurent.vivier/UML/ for further \n"
 "    information.\n\n");
 
+/* Changed only during early boot */
+static int force_sysptvm_disabled = 0;
+
+static int __init nosysptvm_cmd_param(char *str, int* add)
+{
+	force_sysptvm_disabled = 1;
+	return 0;
+}
+
+__uml_setup("nosysptvm", nosysptvm_cmd_param,
+		"nosysptvm\n"
+		"    Turns off syscall emulation tags for ptrace (ptrace_vm) on.\n"
+		"    Ptrace_vm is a feature introduced by Renzo Davoli. It changes\n"
+		"    behaviour of ptrace() and helps reducing host context switch rate.\n"
+		"\n");
+
+static int use_sysemu = 0;
+
+static int __init usesysemu_cmd_param(char *str, int* add)
+{
+	use_sysemu = 1;
+	return 0;
+}
+
+__uml_setup("usesysemu", usesysemu_cmd_param,
+		"usesysemu\n"
+		"    Use sysemu instead of sysptvm even when the kernel supports it.\n\n"
+		);
+
 static void __init check_sysemu(void)
 {
 	unsigned long regs[MAX_REG_NR];
@@ -293,6 +322,102 @@
 	non_fatal("missing\n");
 }
 
+/* test thread code. This thread is started only to test 
+ * which features are provided by the linux kernel */
+static int sysptvm_child(void *arg)
+{
+	int *featurep=arg;
+	int p[2]={-1,-1};
+	pid_t pid=os_getpid();
+	if(ptrace(PTRACE_TRACEME, 0, 0, 0) < 0){
+		perror("ptrace test_ptracemulti");
+		kill(pid, SIGKILL);
+	}
+	kill(pid, SIGSTOP);
+	*featurep=0;
+	os_getpid();
+	/* if it reaches this point in 1 stop it means that
+	 * PTRACE_SYSCALL_SKIPEXIT works */
+	*featurep=PTRACE_SYSCALL_SKIPEXIT;
+	pipe(p);
+	/* if after a PTRACE_SYSCALL_SKIPCALL p[0] is already <0 
+	 * pipe has been really skipped */
+	if (p[0] < 0)
+		*featurep=PTRACE_SYSCALL_SKIPCALL;
+	else { /* clean up everything */
+		close(p[0]);
+		close(p[1]);
+	}
+	return 0;
+}
+
+/* kernel feature test: 
+ * it returns:
+ *   -1 error 
+ *   0 old PTRACE_SYSCALL (addr is ignored)
+ *   PTRACE_SYSCALL_SKIPEXIT: just skip_exit is provided
+ *   PTRACE_SYSCALL_SKIPCALL: the entire syntax is implemented
+ *   by the running kernel */
+static int __init test_ptrace_sysptvm(void) {
+	int pid, status, rv, feature;
+	static char stack[1024];
+	feature=0;
+
+	if((pid = clone(sysptvm_child, &stack[1020], SIGCHLD | CLONE_VM, &feature)) < 0)
+		return 0;
+	if(waitpid(pid, &status, WUNTRACED) < 0){
+		kill(pid, SIGKILL);
+		return 0;
+	}
+	/* restart and wait for the next syscall (getpid)*/
+	rv=ptrace(PTRACE_SYSCALL, pid, 0, 0);
+	if(waitpid(pid, &status, WUNTRACED) < 0)
+		goto out;
+	/* try to skip the exit call */
+	rv=ptrace(PTRACE_SYSCALL, pid, PTRACE_SYSCALL_SKIPEXIT, 0);
+	if (rv < 0)
+		goto out;
+	/* wait for the next stop */
+	if(waitpid(pid, &status, WUNTRACED) < 0)
+		goto out;
+	/* if feature is already 0 it means that this is the exit call,
+	 * and it has not been skipped, otherwise this is the
+	 * entry call for the system call "time" */
+	if (feature<PTRACE_SYSCALL_SKIPEXIT)
+		goto out;
+	/* restart (time) and and try to skip the entire call */
+	rv=ptrace(PTRACE_SYSCALL, pid, PTRACE_SYSCALL_SKIPCALL, 0);
+	if(waitpid(pid, &status, WUNTRACED) < 0)
+		return 0;
+out:
+	ptrace(PTRACE_KILL,pid,0,0);
+	/* eliminate zombie */
+	if(waitpid(pid, &status, WUNTRACED) < 0)
+		return 0;
+	return feature;
+}
+
+static int  __init check_sysptvm(void)
+{
+	int feature=test_ptrace_sysptvm();
+
+	non_fatal("Checking ptrace new tags for syscall emulation...");
+	if (feature==PTRACE_SYSCALL_SKIPCALL) {
+		sysptvm_supported=1;
+		non_fatal("OK");
+		if (!force_sysptvm_disabled) {
+			set_using_sysptvm(PTRACE_SYSCALL_SKIPCALL);
+			non_fatal("\n");
+			return 1;
+		} else {
+			non_fatal(" (disabled)\n");
+			return 0;
+		}
+	} else
+		non_fatal("unsupported\n");
+	return 0;
+}
+
 static void __init check_ptrace(void)
 {
 	int pid, syscall, n, status;
@@ -330,7 +455,8 @@
 	}
 	stop_ptraced_child(pid, 0, 1);
 	non_fatal("OK\n");
-	check_sysemu();
+	if (use_sysemu || !check_sysptvm()) 
+		check_sysemu();
 }
 
 extern void check_tmpexec(void);

[PATCH 2/2] ptrace_vm: ptrace for syscall emulation virtual machines

[Renzo Davoli]

This patch adds the new PTRACE_VM_SKIPCALL and PTRACE_VM_SKIPEXIT
tags for ptrace's addr parameter.
In this way it is possible to (eventually) get rid of PTRACE_SYSEMU
PTRACE_SYSEMU_SINGLESTEP, while providing not only the same features
but a more general support for Virtual Machines.
Part#2: user-mode Linux support. 
User-mode Linux by this patch uses PTRACE_VM of the hosting operating system
and provides PTRACE_VM to its processes.
UML tests at startup which features are provided and uses PTRACE_VM or
PTRACE_SYSEMU (or nothing). PTRACE_VM and/or PTRACE_SYSEMU support can be 
disabled by command line flags.

renzo

Signed-off-by: Renzo Davoli <renzo@cs.unibo.it>
---
diff -Naur linux-2.6.29-rc7-vm1/arch/um/include/shared/kern_util.h linux-2.6.29-rc7-vm2/arch/um/include/shared/kern_util.h
--- linux-2.6.29-rc7-vm1/arch/um/include/shared/kern_util.h	2009-03-06 20:32:34.000000000 +0100
+++ linux-2.6.29-rc7-vm2/arch/um/include/shared/kern_util.h	2009-03-06 20:33:49.000000000 +0100
@@ -57,7 +57,7 @@
 extern unsigned long to_irq_stack(unsigned long *mask_out);
 extern unsigned long from_irq_stack(int nested);
 
-extern void syscall_trace(struct uml_pt_regs *regs, int entryexit);
+extern int syscall_trace(struct uml_pt_regs *regs, int entryexit);
 extern int singlestepping(void *t);
 
 extern void segv_handler(int sig, struct uml_pt_regs *regs);
diff -Naur linux-2.6.29-rc7-vm1/arch/um/include/shared/ptrace_user.h linux-2.6.29-rc7-vm2/arch/um/include/shared/ptrace_user.h
--- linux-2.6.29-rc7-vm1/arch/um/include/shared/ptrace_user.h	2009-03-06 20:32:34.000000000 +0100
+++ linux-2.6.29-rc7-vm2/arch/um/include/shared/ptrace_user.h	2009-03-06 20:33:49.000000000 +0100
@@ -40,9 +40,20 @@
 #define PTRACE_OLDSETOPTIONS PTRACE_SETOPTIONS
 #endif
 
+/* these constant should eventually enter in sys/ptrace.h */
+#ifndef PTRACE_SYSCALL_SKIPCALL
+#define PTRACE_SYSCALL_SKIPCALL      0x6
+#endif
+#ifndef PTRACE_SYSCALL_SKIPEXIT
+#define PTRACE_SYSCALL_SKIPEXIT      0x2
+#endif
+
 void set_using_sysemu(int value);
 int get_using_sysemu(void);
 extern int sysemu_supported;
+void set_using_sysptvm(int value);
+int get_using_sysptvm(void);
+extern int sysptvm_supported;
 
 #define SELECT_PTRACE_OPERATION(sysemu_mode, singlestep_mode) \
 	(((int[3][3] ) { \
diff -Naur linux-2.6.29-rc7-vm1/arch/um/kernel/process.c linux-2.6.29-rc7-vm2/arch/um/kernel/process.c
--- linux-2.6.29-rc7-vm1/arch/um/kernel/process.c	2009-03-06 20:32:34.000000000 +0100
+++ linux-2.6.29-rc7-vm2/arch/um/kernel/process.c	2009-03-06 20:33:49.000000000 +0100
@@ -322,7 +322,9 @@
 }
 
 static atomic_t using_sysemu = ATOMIC_INIT(0);
+static atomic_t using_sysptvm = ATOMIC_INIT(0);
 int sysemu_supported;
+int sysptvm_supported;
 
 void set_using_sysemu(int value)
 {
@@ -336,6 +338,16 @@
 	return atomic_read(&using_sysemu);
 }
 
+void set_using_sysptvm(int value)
+{
+	atomic_set(&using_sysptvm, value);
+}
+
+int get_using_sysptvm(void)
+{
+	return atomic_read(&using_sysptvm);
+}
+
 static int proc_read_sysemu(char *buf, char **start, off_t offset, int size,int *eof, void *data)
 {
 	if (snprintf(buf, size, "%d\n", get_using_sysemu()) < size)
@@ -358,27 +370,63 @@
 	return count;
 }
 
-int __init make_proc_sysemu(void)
+
+static int proc_read_sysptvm(char *buf, char **start, off_t offset, int size,int *eof, void *data)
 {
-	struct proc_dir_entry *ent;
-	if (!sysemu_supported)
-		return 0;
+	int sysptvm=(get_using_sysptvm() != 0);
+	if (snprintf(buf, size, "%d\n", sysptvm) < size)
+		/* No overflow */
+		*eof = 1;
 
-	ent = create_proc_entry("sysemu", 0600, NULL);
+	return strlen(buf);
+}
 
-	if (ent == NULL)
-	{
-		printk(KERN_WARNING "Failed to register /proc/sysemu\n");
-		return 0;
-	}
+static int proc_write_sysptvm(struct file *file,const char __user *buf, unsigned long count,void *data)
+{
+	char tmp[2];
+
+	if (copy_from_user(tmp, buf, 1))
+		return -EFAULT;
+
+	if (tmp[0] == '0')
+		set_using_sysptvm(0);
+	if (tmp[0] == '1')
+		set_using_sysemu(/* XXX */ 6);
+	/* We use the first char, but pretend to write everything */
+	return count;
+}
 
-	ent->read_proc  = proc_read_sysemu;
-	ent->write_proc = proc_write_sysemu;
+int __init make_proc_sysemu_or_sysptvm(void)
+{
+	struct proc_dir_entry *ent;
 
+	if (sysptvm_supported) {
+		ent = create_proc_entry("sysptvm", 0600, NULL);
+
+		if (ent == NULL)
+		{
+			printk(KERN_WARNING "Failed to register /proc/sysptvm\n");
+			return 0;
+		}
+
+		ent->read_proc  = proc_read_sysptvm;
+		ent->write_proc = proc_write_sysptvm;
+	} else if (sysemu_supported) {
+		ent = create_proc_entry("sysemu", 0600, NULL);
+
+		if (ent == NULL)
+		{
+			printk(KERN_WARNING "Failed to register /proc/sysemu\n");
+			return 0;
+		}
+
+		ent->read_proc  = proc_read_sysemu;
+		ent->write_proc = proc_write_sysemu;
+	}
 	return 0;
 }
 
-late_initcall(make_proc_sysemu);
+late_initcall(make_proc_sysemu_or_sysptvm);
 
 int singlestepping(void * t)
 {
diff -Naur linux-2.6.29-rc7-vm1/arch/um/kernel/ptrace.c linux-2.6.29-rc7-vm2/arch/um/kernel/ptrace.c
--- linux-2.6.29-rc7-vm1/arch/um/kernel/ptrace.c	2009-03-06 20:32:34.000000000 +0100
+++ linux-2.6.29-rc7-vm2/arch/um/kernel/ptrace.c	2009-03-06 20:33:49.000000000 +0100
@@ -81,6 +86,8 @@
 		if (request == PTRACE_SYSCALL)
 			set_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 		else clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
+		child->ptrace &= ~PT_SYSCALL_MASK;
+		child->ptrace |= (addr & PTRACE_SYSCALL_MASK) << 28;
 		child->exit_code = data;
 		wake_up_process(child);
 		ret = 0;
@@ -107,7 +114,9 @@
 		ret = -EIO;
 		if (!valid_signal(data))
 			break;
+		child->ptrace &= ~PT_SYSCALL_MASK;
 		clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
+		child->ptrace |= (addr & PTRACE_SYSCALL_MASK) << 28;
 		set_singlestepping(child, 1);
 		child->exit_code = data;
 		/* give it a chance to run. */
@@ -250,7 +259,7 @@
  * XXX Check PT_DTRACE vs TIF_SINGLESTEP for singlestepping check and
  * PT_PTRACED vs TIF_SYSCALL_TRACE for syscall tracing check
  */
-void syscall_trace(struct uml_pt_regs *regs, int entryexit)
+int syscall_trace(struct uml_pt_regs *regs, int entryexit)
 {
 	int is_singlestep = (current->ptrace & PT_DTRACE) && entryexit;
 	int tracesysgood;
@@ -272,10 +281,13 @@
 		send_sigtrap(current, regs, 0);
 
 	if (!test_thread_flag(TIF_SYSCALL_TRACE))
-		return;
+		return 0;
 
 	if (!(current->ptrace & PT_PTRACED))
-		return;
+		return 0;
+
+	if (entryexit && (current->ptrace & PT_SYSCALL_SKIPEXIT))
+		return 0;
 
 	/*
 	 * the 0x80 provides a way for the tracing parent to distinguish
@@ -296,4 +308,8 @@
 		send_sig(current->exit_code, current, 1);
 		current->exit_code = 0;
 	}
+	if (!entryexit && (current->ptrace & PT_SYSCALL_SKIPCALL))
+		return 1;
+	else
+		return 0;
 }
diff -Naur linux-2.6.29-rc7-vm1/arch/um/kernel/skas/syscall.c linux-2.6.29-rc7-vm2/arch/um/kernel/skas/syscall.c
--- linux-2.6.29-rc7-vm1/arch/um/kernel/skas/syscall.c	2009-03-06 20:32:34.000000000 +0100
+++ linux-2.6.29-rc7-vm2/arch/um/kernel/skas/syscall.c	2009-03-06 20:33:49.000000000 +0100
@@ -17,8 +17,9 @@
 	struct pt_regs *regs = container_of(r, struct pt_regs, regs);
 	long result;
 	int syscall;
+	int skip_call;
 
-	syscall_trace(r, 0);
+	skip_call=syscall_trace(r, 0);
 
 	/*
 	 * This should go in the declaration of syscall, but when I do that,
@@ -29,12 +30,14 @@
 	 *     gcc version 4.0.1 20050727 (Red Hat 4.0.1-5)
 	 * in case it's a compiler bug.
 	 */
-	syscall = UPT_SYSCALL_NR(r);
-	if ((syscall >= NR_syscalls) || (syscall < 0))
-		result = -ENOSYS;
-	else result = EXECUTE_SYSCALL(syscall, regs);
+	if (skip_call == 0) {
+		syscall = UPT_SYSCALL_NR(r);
+		if ((syscall >= NR_syscalls) || (syscall < 0))
+			result = -ENOSYS;
+		else result = EXECUTE_SYSCALL(syscall, regs);
 
-	REGS_SET_SYSCALL_RETURN(r->gp, result);
+		REGS_SET_SYSCALL_RETURN(r->gp, result);
+	}
 
 	syscall_trace(r, 1);
 }
diff -Naur linux-2.6.29-rc7-vm1/arch/um/os-Linux/skas/process.c linux-2.6.29-rc7-vm2/arch/um/os-Linux/skas/process.c
--- linux-2.6.29-rc7-vm1/arch/um/os-Linux/skas/process.c	2009-03-06 20:32:34.000000000 +0100
+++ linux-2.6.29-rc7-vm2/arch/um/os-Linux/skas/process.c	2009-03-06 20:33:49.000000000 +0100
@@ -157,7 +157,7 @@
  * (in local_using_sysemu
  */
 static void handle_trap(int pid, struct uml_pt_regs *regs,
-			int local_using_sysemu)
+			int local_using_sysptvm_or_sysemu)
 {
 	int err, status;
 
@@ -167,7 +167,7 @@
 	/* Mark this as a syscall */
 	UPT_SYSCALL_NR(regs) = PT_SYSCALL_NR(regs->gp);
 
-	if (!local_using_sysemu)
+	if (!local_using_sysptvm_or_sysemu)
 	{
 		err = ptrace(PTRACE_POKEUSR, pid, PT_SYSCALL_NR_OFFSET,
 			     __NR_getpid);
@@ -354,6 +354,7 @@
 	int err, status, op, pid = userspace_pid[0];
 	/* To prevent races if using_sysemu changes under us.*/
 	int local_using_sysemu;
+	int local_using_sysptvm;
 
 	if (getitimer(ITIMER_VIRTUAL, &timer))
 		printk(UM_KERN_ERR "Failed to get itimer, errno = %d\n", errno);
@@ -375,11 +376,12 @@
 
 		/* Now we set local_using_sysemu to be used for one loop */
 		local_using_sysemu = get_using_sysemu();
+		local_using_sysptvm = get_using_sysptvm();
 
 		op = SELECT_PTRACE_OPERATION(local_using_sysemu,
 					     singlestepping(NULL));
 
-		if (ptrace(op, pid, 0, 0)) {
+		if (ptrace(op, pid, local_using_sysptvm, 0)) {
 			printk(UM_KERN_ERR "userspace - ptrace continue "
 			       "failed, op = %d, errno = %d\n", op, errno);
 			fatal_sigsegv();
diff -Naur linux-2.6.29-rc7-vm1/arch/um/os-Linux/start_up.c linux-2.6.29-rc7-vm2/arch/um/os-Linux/start_up.c
--- linux-2.6.29-rc7-vm1/arch/um/os-Linux/start_up.c	2009-03-06 20:32:34.000000000 +0100
+++ linux-2.6.29-rc7-vm2/arch/um/os-Linux/start_up.c	2009-03-06 20:33:49.000000000 +0100
@@ -198,6 +198,35 @@
 "    See http://perso.wanadoo.fr/laurent.vivier/UML/ for further \n"
 "    information.\n\n");
 
+/* Changed only during early boot */
+static int force_sysptvm_disabled = 0;
+
+static int __init nosysptvm_cmd_param(char *str, int* add)
+{
+	force_sysptvm_disabled = 1;
+	return 0;
+}
+
+__uml_setup("nosysptvm", nosysptvm_cmd_param,
+		"nosysptvm\n"
+		"    Turns off syscall emulation tags for ptrace (ptrace_vm) on.\n"
+		"    Ptrace_vm is a feature introduced by Renzo Davoli. It changes\n"
+		"    behaviour of ptrace() and helps reducing host context switch rate.\n"
+		"\n");
+
+static int use_sysemu = 0;
+
+static int __init usesysemu_cmd_param(char *str, int* add)
+{
+	use_sysemu = 1;
+	return 0;
+}
+
+__uml_setup("usesysemu", usesysemu_cmd_param,
+		"usesysemu\n"
+		"    Use sysemu instead of sysptvm even when the kernel supports it.\n\n"
+		);
+
 static void __init check_sysemu(void)
 {
 	unsigned long regs[MAX_REG_NR];
@@ -293,6 +322,102 @@
 	non_fatal("missing\n");
 }
 
+/* test thread code. This thread is started only to test 
+ * which features are provided by the linux kernel */
+static int sysptvm_child(void *arg)
+{
+	int *featurep=arg;
+	int p[2]={-1,-1};
+	pid_t pid=os_getpid();
+	if(ptrace(PTRACE_TRACEME, 0, 0, 0) < 0){
+		perror("ptrace test_ptracemulti");
+		kill(pid, SIGKILL);
+	}
+	kill(pid, SIGSTOP);
+	*featurep=0;
+	os_getpid();
+	/* if it reaches this point in 1 stop it means that
+	 * PTRACE_SYSCALL_SKIPEXIT works */
+	*featurep=PTRACE_SYSCALL_SKIPEXIT;
+	pipe(p);
+	/* if after a PTRACE_SYSCALL_SKIPCALL p[0] is already <0 
+	 * pipe has been really skipped */
+	if (p[0] < 0)
+		*featurep=PTRACE_SYSCALL_SKIPCALL;
+	else { /* clean up everything */
+		close(p[0]);
+		close(p[1]);
+	}
+	return 0;
+}
+
+/* kernel feature test: 
+ * it returns:
+ *   -1 error 
+ *   0 old PTRACE_SYSCALL (addr is ignored)
+ *   PTRACE_SYSCALL_SKIPEXIT: just skip_exit is provided
+ *   PTRACE_SYSCALL_SKIPCALL: the entire syntax is implemented
+ *   by the running kernel */
+static int __init test_ptrace_sysptvm(void) {
+	int pid, status, rv, feature;
+	static char stack[1024];
+	feature=0;
+
+	if((pid = clone(sysptvm_child, &stack[1020], SIGCHLD | CLONE_VM, &feature)) < 0)
+		return 0;
+	if(waitpid(pid, &status, WUNTRACED) < 0){
+		kill(pid, SIGKILL);
+		return 0;
+	}
+	/* restart and wait for the next syscall (getpid)*/
+	rv=ptrace(PTRACE_SYSCALL, pid, 0, 0);
+	if(waitpid(pid, &status, WUNTRACED) < 0)
+		goto out;
+	/* try to skip the exit call */
+	rv=ptrace(PTRACE_SYSCALL, pid, PTRACE_SYSCALL_SKIPEXIT, 0);
+	if (rv < 0)
+		goto out;
+	/* wait for the next stop */
+	if(waitpid(pid, &status, WUNTRACED) < 0)
+		goto out;
+	/* if feature is already 0 it means that this is the exit call,
+	 * and it has not been skipped, otherwise this is the
+	 * entry call for the system call "time" */
+	if (feature<PTRACE_SYSCALL_SKIPEXIT)
+		goto out;
+	/* restart (time) and and try to skip the entire call */
+	rv=ptrace(PTRACE_SYSCALL, pid, PTRACE_SYSCALL_SKIPCALL, 0);
+	if(waitpid(pid, &status, WUNTRACED) < 0)
+		return 0;
+out:
+	ptrace(PTRACE_KILL,pid,0,0);
+	/* eliminate zombie */
+	if(waitpid(pid, &status, WUNTRACED) < 0)
+		return 0;
+	return feature;
+}
+
+static int  __init check_sysptvm(void)
+{
+	int feature=test_ptrace_sysptvm();
+
+	non_fatal("Checking ptrace new tags for syscall emulation...");
+	if (feature==PTRACE_SYSCALL_SKIPCALL) {
+		sysptvm_supported=1;
+		non_fatal("OK");
+		if (!force_sysptvm_disabled) {
+			set_using_sysptvm(PTRACE_SYSCALL_SKIPCALL);
+			non_fatal("\n");
+			return 1;
+		} else {
+			non_fatal(" (disabled)\n");
+			return 0;
+		}
+	} else
+		non_fatal("unsupported\n");
+	return 0;
+}
+
 static void __init check_ptrace(void)
 {
 	int pid, syscall, n, status;
@@ -330,7 +455,8 @@
 	}
 	stop_ptraced_child(pid, 0, 1);
 	non_fatal("OK\n");
-	check_sysemu();
+	if (use_sysemu || !check_sysptvm()) 
+		check_sysemu();
 }
 
 extern void check_tmpexec(void);

Re: [PATCH 2/2] ptrace_vm: ptrace for syscall emulation virtual machines

[Ingo Molnar]

* Renzo Davoli <renzo@cs.unibo.it> wrote:

> +/* test thread code. This thread is started only to test 
> + * which features are provided by the linux kernel */
> +static int sysptvm_child(void *arg)
> +{
> +	int *featurep=arg;
> +	int p[2]={-1,-1};
> +	pid_t pid=os_getpid();
> +	if(ptrace(PTRACE_TRACEME, 0, 0, 0) < 0){
> +		perror("ptrace test_ptracemulti");
> +		kill(pid, SIGKILL);
> +	}
> +	kill(pid, SIGSTOP);
> +	*featurep=0;
> +	os_getpid();
> +	/* if it reaches this point in 1 stop it means that
> +	 * PTRACE_SYSCALL_SKIPEXIT works */
> +	*featurep=PTRACE_SYSCALL_SKIPEXIT;
> +	pipe(p);
> +	/* if after a PTRACE_SYSCALL_SKIPCALL p[0] is already <0 
> +	 * pipe has been really skipped */
> +	if (p[0] < 0)
> +		*featurep=PTRACE_SYSCALL_SKIPCALL;
> +	else { /* clean up everything */
> +		close(p[0]);
> +		close(p[1]);
> +	}
> +	return 0;

Please check Documentation/CodingStyle. Every second line above 
violates it. scripts/checkpatch.pl can help out with the more 
obvious ones.

	Ingo

Re: [PATCH 2/2] ptrace_vm: ptrace for syscall emulation virtual machines

[Renzo Davoli]

> Please check Documentation/CodingStyle. Every second line above 
> violates it. scripts/checkpatch.pl can help out with the more 
> obvious ones.
Ingo, 

Thank you for your comment.
You are right, I beg your pardon.
I have updated the patch, now it should be (more) consistent
with the Coding Style specifications.

This patch adds the new PTRACE_VM_SKIPCALL and PTRACE_VM_SKIPEXIT
tags for ptrace's addr parameter.
In this way it is possible to (eventually) get rid of PTRACE_SYSEMU
PTRACE_SYSEMU_SINGLESTEP, while providing not only the same features
but a more general support for Virtual Machines.
Part#2: user-mode Linux support.
User-mode Linux by this patch uses PTRACE_VM of the hosting operating system
and provides PTRACE_VM to its processes.
UML tests at startup which features are provided and uses PTRACE_VM or
PTRACE_SYSEMU (or nothing). PTRACE_VM and/or PTRACE_SYSEMU support can be
disabled by command line flags.

renzo

Signed-off-by: Renzo Davoli <renzo@cs.unibo.it>
----
diff -Naur linux-2.6.29-rc7-git4/arch/um/include/shared/kern_util.h linux-2.6.29-rc7-git4.vm2/arch/um/include/shared/kern_util.h
--- linux-2.6.29-rc7-git4/arch/um/include/shared/kern_util.h	2009-03-11 09:25:27.000000000 +0100
+++ linux-2.6.29-rc7-git4.vm2/arch/um/include/shared/kern_util.h	2009-03-11 09:35:23.000000000 +0100
@@ -57,7 +57,7 @@
 extern unsigned long to_irq_stack(unsigned long *mask_out);
 extern unsigned long from_irq_stack(int nested);
 
-extern void syscall_trace(struct uml_pt_regs *regs, int entryexit);
+extern int syscall_trace(struct uml_pt_regs *regs, int entryexit);
 extern int singlestepping(void *t);
 
 extern void segv_handler(int sig, struct uml_pt_regs *regs);
diff -Naur linux-2.6.29-rc7-git4/arch/um/include/shared/ptrace_user.h linux-2.6.29-rc7-git4.vm2/arch/um/include/shared/ptrace_user.h
--- linux-2.6.29-rc7-git4/arch/um/include/shared/ptrace_user.h	2009-03-11 09:25:27.000000000 +0100
+++ linux-2.6.29-rc7-git4.vm2/arch/um/include/shared/ptrace_user.h	2009-03-11 09:35:23.000000000 +0100
@@ -40,9 +40,20 @@
 #define PTRACE_OLDSETOPTIONS PTRACE_SETOPTIONS
 #endif
 
+/* these constant should eventually enter in sys/ptrace.h */
+#ifndef PTRACE_SYSCALL_SKIPCALL
+#define PTRACE_SYSCALL_SKIPCALL      0x6
+#endif
+#ifndef PTRACE_SYSCALL_SKIPEXIT
+#define PTRACE_SYSCALL_SKIPEXIT      0x2
+#endif
+
 void set_using_sysemu(int value);
 int get_using_sysemu(void);
 extern int sysemu_supported;
+void set_using_sysptvm(int value);
+int get_using_sysptvm(void);
+extern int sysptvm_supported;
 
 #define SELECT_PTRACE_OPERATION(sysemu_mode, singlestep_mode) \
 	(((int[3][3] ) { \
diff -Naur linux-2.6.29-rc7-git4/arch/um/kernel/process.c linux-2.6.29-rc7-git4.vm2/arch/um/kernel/process.c
--- linux-2.6.29-rc7-git4/arch/um/kernel/process.c	2009-03-11 09:25:27.000000000 +0100
+++ linux-2.6.29-rc7-git4.vm2/arch/um/kernel/process.c	2009-03-11 10:03:05.000000000 +0100
@@ -322,7 +322,9 @@
 }
 
 static atomic_t using_sysemu = ATOMIC_INIT(0);
+static atomic_t using_sysptvm = ATOMIC_INIT(0);
 int sysemu_supported;
+int sysptvm_supported;
 
 void set_using_sysemu(int value)
 {
@@ -336,7 +338,18 @@
 	return atomic_read(&using_sysemu);
 }
 
-static int proc_read_sysemu(char *buf, char **start, off_t offset, int size,int *eof, void *data)
+void set_using_sysptvm(int value)
+{
+	atomic_set(&using_sysptvm, value);
+}
+
+int get_using_sysptvm(void)
+{
+	return atomic_read(&using_sysptvm);
+}
+
+static int proc_read_sysemu(char *buf, char **start, off_t offset,
+		int size, int *eof, void *data)
 {
 	if (snprintf(buf, size, "%d\n", get_using_sysemu()) < size)
 		/* No overflow */
@@ -345,7 +358,8 @@
 	return strlen(buf);
 }
 
-static int proc_write_sysemu(struct file *file,const char __user *buf, unsigned long count,void *data)
+static int proc_write_sysemu(struct file *file, const char __user *buf,
+		unsigned long count, void *data)
 {
 	char tmp[2];
 
@@ -358,27 +372,63 @@
 	return count;
 }
 
-int __init make_proc_sysemu(void)
+
+static int proc_read_sysptvm(char *buf, char **start, off_t offset,
+		int size, int *eof, void *data)
 {
-	struct proc_dir_entry *ent;
-	if (!sysemu_supported)
-		return 0;
+	int sysptvm = (get_using_sysptvm() != 0);
+	if (snprintf(buf, size, "%d\n", sysptvm) < size)
+		/* No overflow */
+		*eof = 1;
 
-	ent = create_proc_entry("sysemu", 0600, NULL);
+	return strlen(buf);
+}
 
-	if (ent == NULL)
-	{
-		printk(KERN_WARNING "Failed to register /proc/sysemu\n");
-		return 0;
-	}
+static int proc_write_sysptvm(struct file *file, const char __user *buf,
+		unsigned long count, void *data)
+{
+	char tmp[2];
+
+	if (copy_from_user(tmp, buf, 1))
+		return -EFAULT;
+
+	if (tmp[0] == '0')
+		set_using_sysptvm(0);
+	if (tmp[0] == '1')
+		set_using_sysemu(/* XXX */ 6);
+	/* We use the first char, but pretend to write everything */
+	return count;
+}
 
-	ent->read_proc  = proc_read_sysemu;
-	ent->write_proc = proc_write_sysemu;
+int __init make_proc_sysemu_or_sysptvm(void)
+{
+	struct proc_dir_entry *ent;
 
+	if (sysptvm_supported) {
+		ent = create_proc_entry("sysptvm", 0600, NULL);
+
+		if (ent == NULL) {
+			printk(KERN_WARNING "Failed to register /proc/sysptvm\n");
+			return 0;
+		}
+
+		ent->read_proc  = proc_read_sysptvm;
+		ent->write_proc = proc_write_sysptvm;
+	} else if (sysemu_supported) {
+		ent = create_proc_entry("sysemu", 0600, NULL);
+
+		if (ent == NULL) {
+			printk(KERN_WARNING "Failed to register /proc/sysemu\n");
+			return 0;
+		}
+
+		ent->read_proc  = proc_read_sysemu;
+		ent->write_proc = proc_write_sysemu;
+	}
 	return 0;
 }
 
-late_initcall(make_proc_sysemu);
+late_initcall(make_proc_sysemu_or_sysptvm);
 
 int singlestepping(void * t)
 {
diff -Naur linux-2.6.29-rc7-git4/arch/um/kernel/ptrace.c linux-2.6.29-rc7-git4.vm2/arch/um/kernel/ptrace.c
--- linux-2.6.29-rc7-git4/arch/um/kernel/ptrace.c	2009-03-11 09:30:19.000000000 +0100
+++ linux-2.6.29-rc7-git4.vm2/arch/um/kernel/ptrace.c	2009-03-11 09:35:23.000000000 +0100
@@ -81,6 +81,8 @@
 		if (request == PTRACE_SYSCALL)
 			set_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 		else clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
+		child->ptrace &= ~PT_SYSCALL_MASK;
+		child->ptrace |= (addr & PTRACE_SYSCALL_MASK) << 28;
 		child->exit_code = data;
 		wake_up_process(child);
 		ret = 0;
@@ -107,7 +109,9 @@
 		ret = -EIO;
 		if (!valid_signal(data))
 			break;
+		child->ptrace &= ~PT_SYSCALL_MASK;
 		clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
+		child->ptrace |= (addr & PTRACE_SYSCALL_MASK) << 28;
 		set_singlestepping(child, 1);
 		child->exit_code = data;
 		/* give it a chance to run. */
@@ -250,7 +254,7 @@
  * XXX Check PT_DTRACE vs TIF_SINGLESTEP for singlestepping check and
  * PT_PTRACED vs TIF_SYSCALL_TRACE for syscall tracing check
  */
-void syscall_trace(struct uml_pt_regs *regs, int entryexit)
+int syscall_trace(struct uml_pt_regs *regs, int entryexit)
 {
 	int is_singlestep = (current->ptrace & PT_DTRACE) && entryexit;
 	int tracesysgood;
@@ -272,10 +276,13 @@
 		send_sigtrap(current, regs, 0);
 
 	if (!test_thread_flag(TIF_SYSCALL_TRACE))
-		return;
+		return 0;
 
 	if (!(current->ptrace & PT_PTRACED))
-		return;
+		return 0;
+
+	if (entryexit && (current->ptrace & PT_SYSCALL_SKIPEXIT))
+		return 0;
 
 	/*
 	 * the 0x80 provides a way for the tracing parent to distinguish
@@ -296,4 +303,8 @@
 		send_sig(current->exit_code, current, 1);
 		current->exit_code = 0;
 	}
+	if (!entryexit && (current->ptrace & PT_SYSCALL_SKIPCALL))
+		return 1;
+	else
+		return 0;
 }
diff -Naur linux-2.6.29-rc7-git4/arch/um/kernel/skas/syscall.c linux-2.6.29-rc7-git4.vm2/arch/um/kernel/skas/syscall.c
--- linux-2.6.29-rc7-git4/arch/um/kernel/skas/syscall.c	2009-03-11 09:25:27.000000000 +0100
+++ linux-2.6.29-rc7-git4.vm2/arch/um/kernel/skas/syscall.c	2009-03-11 09:41:29.000000000 +0100
@@ -17,8 +17,9 @@
 	struct pt_regs *regs = container_of(r, struct pt_regs, regs);
 	long result;
 	int syscall;
+	int skip_call;
 
-	syscall_trace(r, 0);
+	skip_call = syscall_trace(r, 0);
 
 	/*
 	 * This should go in the declaration of syscall, but when I do that,
@@ -29,12 +30,15 @@
 	 *     gcc version 4.0.1 20050727 (Red Hat 4.0.1-5)
 	 * in case it's a compiler bug.
 	 */
-	syscall = UPT_SYSCALL_NR(r);
-	if ((syscall >= NR_syscalls) || (syscall < 0))
-		result = -ENOSYS;
-	else result = EXECUTE_SYSCALL(syscall, regs);
+	if (skip_call == 0) {
+		syscall = UPT_SYSCALL_NR(r);
+		if ((syscall >= NR_syscalls) || (syscall < 0))
+			result = -ENOSYS;
+		else
+			result = EXECUTE_SYSCALL(syscall, regs);
 
-	REGS_SET_SYSCALL_RETURN(r->gp, result);
+		REGS_SET_SYSCALL_RETURN(r->gp, result);
+	}
 
 	syscall_trace(r, 1);
 }
diff -Naur linux-2.6.29-rc7-git4/arch/um/os-Linux/skas/process.c linux-2.6.29-rc7-git4.vm2/arch/um/os-Linux/skas/process.c
--- linux-2.6.29-rc7-git4/arch/um/os-Linux/skas/process.c	2009-03-11 09:25:27.000000000 +0100
+++ linux-2.6.29-rc7-git4.vm2/arch/um/os-Linux/skas/process.c	2009-03-11 09:35:23.000000000 +0100
@@ -157,7 +157,7 @@
  * (in local_using_sysemu
  */
 static void handle_trap(int pid, struct uml_pt_regs *regs,
-			int local_using_sysemu)
+			int local_using_sysptvm_or_sysemu)
 {
 	int err, status;
 
@@ -167,7 +167,7 @@
 	/* Mark this as a syscall */
 	UPT_SYSCALL_NR(regs) = PT_SYSCALL_NR(regs->gp);
 
-	if (!local_using_sysemu)
+	if (!local_using_sysptvm_or_sysemu)
 	{
 		err = ptrace(PTRACE_POKEUSR, pid, PT_SYSCALL_NR_OFFSET,
 			     __NR_getpid);
@@ -354,6 +354,7 @@
 	int err, status, op, pid = userspace_pid[0];
 	/* To prevent races if using_sysemu changes under us.*/
 	int local_using_sysemu;
+	int local_using_sysptvm;
 
 	if (getitimer(ITIMER_VIRTUAL, &timer))
 		printk(UM_KERN_ERR "Failed to get itimer, errno = %d\n", errno);
@@ -375,11 +376,12 @@
 
 		/* Now we set local_using_sysemu to be used for one loop */
 		local_using_sysemu = get_using_sysemu();
+		local_using_sysptvm = get_using_sysptvm();
 
 		op = SELECT_PTRACE_OPERATION(local_using_sysemu,
 					     singlestepping(NULL));
 
-		if (ptrace(op, pid, 0, 0)) {
+		if (ptrace(op, pid, local_using_sysptvm, 0)) {
 			printk(UM_KERN_ERR "userspace - ptrace continue "
 			       "failed, op = %d, errno = %d\n", op, errno);
 			fatal_sigsegv();
diff -Naur linux-2.6.29-rc7-git4/arch/um/os-Linux/start_up.c linux-2.6.29-rc7-git4.vm2/arch/um/os-Linux/start_up.c
--- linux-2.6.29-rc7-git4/arch/um/os-Linux/start_up.c	2009-03-11 09:25:27.000000000 +0100
+++ linux-2.6.29-rc7-git4.vm2/arch/um/os-Linux/start_up.c	2009-03-11 09:58:40.000000000 +0100
@@ -198,6 +198,34 @@
 "    See http://perso.wanadoo.fr/laurent.vivier/UML/ for further \n"
 "    information.\n\n");
 
+/* Changed only during early boot */
+static int force_sysptvm_disabled;
+
+static int __init nosysptvm_cmd_param(char *str, int* add)
+{
+	force_sysptvm_disabled = 1;
+	return 0;
+}
+
+__uml_setup("nosysptvm", nosysptvm_cmd_param,
+"nosysptvm\n"
+"    Turns off syscall emulation tags for ptrace (ptrace_vm) on.\n"
+"    Ptrace_vm is a feature introduced by Renzo Davoli. It changes\n"
+"    behaviour of ptrace() and helps reducing host context switch rate.\n\n");
+
+static int use_sysemu;
+
+static int __init usesysemu_cmd_param(char *str, int* add)
+{
+	use_sysemu = 1;
+	return 0;
+}
+
+__uml_setup("usesysemu", usesysemu_cmd_param,
+"usesysemu\n"
+"    Use sysemu instead of sysptvm even when the kernel supports it.\n\n"
+);
+
 static void __init check_sysemu(void)
 {
 	unsigned long regs[MAX_REG_NR];
@@ -293,6 +321,114 @@
 	non_fatal("missing\n");
 }
 
+/*
+ * test thread code. This thread is started only to test
+ * which features are provided by the linux kernel
+ */
+static int sysptvm_child(void *arg)
+{
+	int *featurep = arg;
+	int p[2] = {-1, -1};
+	pid_t pid = os_getpid();
+	if (ptrace(PTRACE_TRACEME, 0, 0, 0) < 0) {
+		perror("ptrace test_ptracemulti");
+		kill(pid, SIGKILL);
+	}
+	kill(pid, SIGSTOP);
+	*featurep = 0;
+	os_getpid();
+	/*
+	 * if it reaches this point in 1 stop it means that
+	 * PTRACE_SYSCALL_SKIPEXIT works
+	 */
+	*featurep = PTRACE_SYSCALL_SKIPEXIT;
+	pipe(p);
+	/*
+	 * if after a PTRACE_SYSCALL_SKIPCALL p[0] is already <0
+	 * pipe has been really skipped
+	 */
+	if (p[0] < 0)
+		*featurep = PTRACE_SYSCALL_SKIPCALL;
+	else { /* clean up everything */
+		close(p[0]);
+		close(p[1]);
+	}
+	return 0;
+}
+
+/*
+ * kernel feature test:
+ * it returns:
+ *   -1 error
+ *   0 old PTRACE_SYSCALL (addr is ignored)
+ *   PTRACE_SYSCALL_SKIPEXIT: just skip_exit is provided
+ *   PTRACE_SYSCALL_SKIPCALL: the entire syntax is implemented
+ *   by the running kernel
+ */
+static int __init test_ptrace_sysptvm(void)
+{
+	int pid, status, rv, feature;
+	static char stack[1024];
+	feature = 0;
+
+	pid = clone(sysptvm_child, &stack[1020], SIGCHLD | CLONE_VM, &feature);
+	if (pid < 0)
+		return 0;
+	if (waitpid(pid, &status, WUNTRACED) < 0) {
+		kill(pid, SIGKILL);
+		return 0;
+	}
+	/* restart and wait for the next syscall (getpid)*/
+	rv = ptrace(PTRACE_SYSCALL, pid, 0, 0);
+	if (waitpid(pid, &status, WUNTRACED) < 0)
+		goto out;
+	/* try to skip the exit call */
+	rv = ptrace(PTRACE_SYSCALL, pid, PTRACE_SYSCALL_SKIPEXIT, 0);
+	if (rv < 0)
+		goto out;
+	/* wait for the next stop */
+	if (waitpid(pid, &status, WUNTRACED) < 0)
+		goto out;
+	/*
+	 * if feature is already 0 it means that this is the exit call,
+	 * and it has not been skipped, otherwise this is the
+	 * entry call for the system call "time"
+	 */
+	if (feature < PTRACE_SYSCALL_SKIPEXIT)
+		goto out;
+	/* restart (time) and and try to skip the entire call */
+	rv = ptrace(PTRACE_SYSCALL, pid, PTRACE_SYSCALL_SKIPCALL, 0);
+	if (waitpid(pid, &status, WUNTRACED) < 0)
+		return 0;
+out:
+	ptrace(PTRACE_KILL, pid, 0, 0);
+	/* eliminate zombie */
+	if (waitpid(pid, &status, WUNTRACED) < 0)
+		return 0;
+	return feature;
+}
+
+static int  __init check_sysptvm(void)
+{
+	int feature = test_ptrace_sysptvm();
+
+	non_fatal("Checking ptrace new tags for syscall emulation...");
+	if (feature == PTRACE_SYSCALL_SKIPCALL) {
+		sysptvm_supported = 1;
+		non_fatal("OK");
+		if (!force_sysptvm_disabled) {
+			set_using_sysptvm(PTRACE_SYSCALL_SKIPCALL);
+			non_fatal("\n");
+			return 1;
+		} else {
+			non_fatal(" (disabled)\n");
+			return 0;
+		}
+	} else
+		non_fatal("unsupported\n");
+	return 0;
+}
+
 static void __init check_ptrace(void)
 {
 	int pid, syscall, n, status;
@@ -330,7 +466,8 @@
 	}
 	stop_ptraced_child(pid, 0, 1);
 	non_fatal("OK\n");
-	check_sysemu();
+	if (use_sysemu || !check_sysptvm())
+		check_sysemu();
 }
 
 extern void check_tmpexec(void);

Re: [PATCH 2/2] ptrace_vm: ptrace for syscall emulation virtual machines

[Américo Wang]

On Wed, Mar 11, 2009 at 02:41:38PM +0100, Renzo Davoli wrote:
>> Please check Documentation/CodingStyle. Every second line above 
>> violates it. scripts/checkpatch.pl can help out with the more 
>> obvious ones.
>Ingo, 
>
>Thank you for your comment.
>You are right, I beg your pardon.
>I have updated the patch, now it should be (more) consistent
>with the Coding Style specifications.

You can use scripts/checkpatch.pl to check it before sending.

>
>This patch adds the new PTRACE_VM_SKIPCALL and PTRACE_VM_SKIPEXIT
>tags for ptrace's addr parameter.
>In this way it is possible to (eventually) get rid of PTRACE_SYSEMU
>PTRACE_SYSEMU_SINGLESTEP, while providing not only the same features
>but a more general support for Virtual Machines.
>Part#2: user-mode Linux support.
>User-mode Linux by this patch uses PTRACE_VM of the hosting operating system
>and provides PTRACE_VM to its processes.
>UML tests at startup which features are provided and uses PTRACE_VM or
>PTRACE_SYSEMU (or nothing). PTRACE_VM and/or PTRACE_SYSEMU support can be
>disabled by command line flags.
>

So what? PTRACE_VM is only supported in UML with this patch,
UML still has to use PTRACE_SYSEMU on x86_32.

Am I missing something? :)


>
>Signed-off-by: Renzo Davoli <renzo@cs.unibo.it>


Minor comments below.

>----
>diff -Naur linux-2.6.29-rc7-git4/arch/um/include/shared/kern_util.h linux-2.6.29-rc7-git4.vm2/arch/um/include/shared/kern_util.h
>--- linux-2.6.29-rc7-git4/arch/um/include/shared/kern_util.h	2009-03-11 09:25:27.000000000 +0100
>+++ linux-2.6.29-rc7-git4.vm2/arch/um/include/shared/kern_util.h	2009-03-11 09:35:23.000000000 +0100
>@@ -57,7 +57,7 @@
> extern unsigned long to_irq_stack(unsigned long *mask_out);
> extern unsigned long from_irq_stack(int nested);
> 
>-extern void syscall_trace(struct uml_pt_regs *regs, int entryexit);
>+extern int syscall_trace(struct uml_pt_regs *regs, int entryexit);
> extern int singlestepping(void *t);
> 
> extern void segv_handler(int sig, struct uml_pt_regs *regs);
>diff -Naur linux-2.6.29-rc7-git4/arch/um/include/shared/ptrace_user.h linux-2.6.29-rc7-git4.vm2/arch/um/include/shared/ptrace_user.h
>--- linux-2.6.29-rc7-git4/arch/um/include/shared/ptrace_user.h	2009-03-11 09:25:27.000000000 +0100
>+++ linux-2.6.29-rc7-git4.vm2/arch/um/include/shared/ptrace_user.h	2009-03-11 09:35:23.000000000 +0100
>@@ -40,9 +40,20 @@
> #define PTRACE_OLDSETOPTIONS PTRACE_SETOPTIONS
> #endif
> 
>+/* these constant should eventually enter in sys/ptrace.h */
>+#ifndef PTRACE_SYSCALL_SKIPCALL
>+#define PTRACE_SYSCALL_SKIPCALL      0x6
>+#endif
>+#ifndef PTRACE_SYSCALL_SKIPEXIT
>+#define PTRACE_SYSCALL_SKIPEXIT      0x2
>+#endif
>+
> void set_using_sysemu(int value);
> int get_using_sysemu(void);
> extern int sysemu_supported;
>+void set_using_sysptvm(int value);
>+int get_using_sysptvm(void);
>+extern int sysptvm_supported;
> 
> #define SELECT_PTRACE_OPERATION(sysemu_mode, singlestep_mode) \
> 	(((int[3][3] ) { \
>diff -Naur linux-2.6.29-rc7-git4/arch/um/kernel/process.c linux-2.6.29-rc7-git4.vm2/arch/um/kernel/process.c
>--- linux-2.6.29-rc7-git4/arch/um/kernel/process.c	2009-03-11 09:25:27.000000000 +0100
>+++ linux-2.6.29-rc7-git4.vm2/arch/um/kernel/process.c	2009-03-11 10:03:05.000000000 +0100
>@@ -322,7 +322,9 @@
> }
> 
> static atomic_t using_sysemu = ATOMIC_INIT(0);
>+static atomic_t using_sysptvm = ATOMIC_INIT(0);
> int sysemu_supported;
>+int sysptvm_supported;
> 
> void set_using_sysemu(int value)
> {
>@@ -336,7 +338,18 @@
> 	return atomic_read(&using_sysemu);
> }
> 
>-static int proc_read_sysemu(char *buf, char **start, off_t offset, int size,int *eof, void *data)
>+void set_using_sysptvm(int value)
>+{
>+	atomic_set(&using_sysptvm, value);
>+}
>+
>+int get_using_sysptvm(void)
>+{
>+	return atomic_read(&using_sysptvm);
>+}


How about making it boolean? AFAIK, you use it as a boolean.


>+
>+static int proc_read_sysemu(char *buf, char **start, off_t offset,
>+		int size, int *eof, void *data)
> {
> 	if (snprintf(buf, size, "%d\n", get_using_sysemu()) < size)
> 		/* No overflow */
>@@ -345,7 +358,8 @@
> 	return strlen(buf);
> }
> 
>-static int proc_write_sysemu(struct file *file,const char __user *buf, unsigned long count,void *data)
>+static int proc_write_sysemu(struct file *file, const char __user *buf,
>+		unsigned long count, void *data)
> {
> 	char tmp[2];
> 
>@@ -358,27 +372,63 @@
> 	return count;
> }
> 
>-int __init make_proc_sysemu(void)
>+
>+static int proc_read_sysptvm(char *buf, char **start, off_t offset,
>+		int size, int *eof, void *data)
> {
>-	struct proc_dir_entry *ent;
>-	if (!sysemu_supported)
>-		return 0;
>+	int sysptvm = (get_using_sysptvm() != 0);
>+	if (snprintf(buf, size, "%d\n", sysptvm) < size)
>+		/* No overflow */
>+		*eof = 1;
> 
>-	ent = create_proc_entry("sysemu", 0600, NULL);
>+	return strlen(buf);
>+}
> 
>-	if (ent == NULL)
>-	{
>-		printk(KERN_WARNING "Failed to register /proc/sysemu\n");
>-		return 0;
>-	}
>+static int proc_write_sysptvm(struct file *file, const char __user *buf,
>+		unsigned long count, void *data)
>+{
>+	char tmp[2];
>+
>+	if (copy_from_user(tmp, buf, 1))
>+		return -EFAULT;
>+
>+	if (tmp[0] == '0')
>+		set_using_sysptvm(0);
>+	if (tmp[0] == '1')
>+		set_using_sysemu(/* XXX */ 6);
>+	/* We use the first char, but pretend to write everything */
>+	return count;
>+}
> 
>-	ent->read_proc  = proc_read_sysemu;
>-	ent->write_proc = proc_write_sysemu;
>+int __init make_proc_sysemu_or_sysptvm(void)
>+{
>+	struct proc_dir_entry *ent;
> 
>+	if (sysptvm_supported) {
>+		ent = create_proc_entry("sysptvm", 0600, NULL);
>+
>+		if (ent == NULL) {
>+			printk(KERN_WARNING "Failed to register /proc/sysptvm\n");
>+			return 0;
>+		}
>+
>+		ent->read_proc  = proc_read_sysptvm;
>+		ent->write_proc = proc_write_sysptvm;
>+	} else if (sysemu_supported) {
>+		ent = create_proc_entry("sysemu", 0600, NULL);
>+
>+		if (ent == NULL) {
>+			printk(KERN_WARNING "Failed to register /proc/sysemu\n");
>+			return 0;
>+		}
>+
>+		ent->read_proc  = proc_read_sysemu;
>+		ent->write_proc = proc_write_sysemu;
>+	}
> 	return 0;
> }
> 
>-late_initcall(make_proc_sysemu);
>+late_initcall(make_proc_sysemu_or_sysptvm);
> 
> int singlestepping(void * t)
> {
>diff -Naur linux-2.6.29-rc7-git4/arch/um/kernel/ptrace.c linux-2.6.29-rc7-git4.vm2/arch/um/kernel/ptrace.c
>--- linux-2.6.29-rc7-git4/arch/um/kernel/ptrace.c	2009-03-11 09:30:19.000000000 +0100
>+++ linux-2.6.29-rc7-git4.vm2/arch/um/kernel/ptrace.c	2009-03-11 09:35:23.000000000 +0100
>@@ -81,6 +81,8 @@
> 		if (request == PTRACE_SYSCALL)
> 			set_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
> 		else clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
>+		child->ptrace &= ~PT_SYSCALL_MASK;
>+		child->ptrace |= (addr & PTRACE_SYSCALL_MASK) << 28;

28, ditto.

> 		child->exit_code = data;
> 		wake_up_process(child);
> 		ret = 0;
>@@ -107,7 +109,9 @@
> 		ret = -EIO;
> 		if (!valid_signal(data))
> 			break;
>+		child->ptrace &= ~PT_SYSCALL_MASK;
> 		clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
>+		child->ptrace |= (addr & PTRACE_SYSCALL_MASK) << 28;
> 		set_singlestepping(child, 1);
> 		child->exit_code = data;
> 		/* give it a chance to run. */
>@@ -250,7 +254,7 @@
>  * XXX Check PT_DTRACE vs TIF_SINGLESTEP for singlestepping check and
>  * PT_PTRACED vs TIF_SYSCALL_TRACE for syscall tracing check
>  */
>-void syscall_trace(struct uml_pt_regs *regs, int entryexit)
>+int syscall_trace(struct uml_pt_regs *regs, int entryexit)
> {
> 	int is_singlestep = (current->ptrace & PT_DTRACE) && entryexit;
> 	int tracesysgood;
>@@ -272,10 +276,13 @@
> 		send_sigtrap(current, regs, 0);
> 
> 	if (!test_thread_flag(TIF_SYSCALL_TRACE))
>-		return;
>+		return 0;
> 
> 	if (!(current->ptrace & PT_PTRACED))
>-		return;
>+		return 0;
>+
>+	if (entryexit && (current->ptrace & PT_SYSCALL_SKIPEXIT))
>+		return 0;
> 
> 	/*
> 	 * the 0x80 provides a way for the tracing parent to distinguish
>@@ -296,4 +303,8 @@
> 		send_sig(current->exit_code, current, 1);
> 		current->exit_code = 0;
> 	}
>+	if (!entryexit && (current->ptrace & PT_SYSCALL_SKIPCALL))
>+		return 1;
>+	else
>+		return 0;
> }
>diff -Naur linux-2.6.29-rc7-git4/arch/um/kernel/skas/syscall.c linux-2.6.29-rc7-git4.vm2/arch/um/kernel/skas/syscall.c
>--- linux-2.6.29-rc7-git4/arch/um/kernel/skas/syscall.c	2009-03-11 09:25:27.000000000 +0100
>+++ linux-2.6.29-rc7-git4.vm2/arch/um/kernel/skas/syscall.c	2009-03-11 09:41:29.000000000 +0100
>@@ -17,8 +17,9 @@
> 	struct pt_regs *regs = container_of(r, struct pt_regs, regs);
> 	long result;
> 	int syscall;
>+	int skip_call;
> 
>-	syscall_trace(r, 0);
>+	skip_call = syscall_trace(r, 0);
> 
> 	/*
> 	 * This should go in the declaration of syscall, but when I do that,
>@@ -29,12 +30,15 @@
> 	 *     gcc version 4.0.1 20050727 (Red Hat 4.0.1-5)
> 	 * in case it's a compiler bug.
> 	 */
>-	syscall = UPT_SYSCALL_NR(r);
>-	if ((syscall >= NR_syscalls) || (syscall < 0))
>-		result = -ENOSYS;
>-	else result = EXECUTE_SYSCALL(syscall, regs);
>+	if (skip_call == 0) {
>+		syscall = UPT_SYSCALL_NR(r);
>+		if ((syscall >= NR_syscalls) || (syscall < 0))
>+			result = -ENOSYS;
>+		else
>+			result = EXECUTE_SYSCALL(syscall, regs);
> 
>-	REGS_SET_SYSCALL_RETURN(r->gp, result);
>+		REGS_SET_SYSCALL_RETURN(r->gp, result);
>+	}
> 
> 	syscall_trace(r, 1);
> }
>diff -Naur linux-2.6.29-rc7-git4/arch/um/os-Linux/skas/process.c linux-2.6.29-rc7-git4.vm2/arch/um/os-Linux/skas/process.c
>--- linux-2.6.29-rc7-git4/arch/um/os-Linux/skas/process.c	2009-03-11 09:25:27.000000000 +0100
>+++ linux-2.6.29-rc7-git4.vm2/arch/um/os-Linux/skas/process.c	2009-03-11 09:35:23.000000000 +0100
>@@ -157,7 +157,7 @@
>  * (in local_using_sysemu
>  */
> static void handle_trap(int pid, struct uml_pt_regs *regs,
>-			int local_using_sysemu)
>+			int local_using_sysptvm_or_sysemu)


This argument name is too long. :)


> {
> 	int err, status;
> 
>@@ -167,7 +167,7 @@
> 	/* Mark this as a syscall */
> 	UPT_SYSCALL_NR(regs) = PT_SYSCALL_NR(regs->gp);
> 
>-	if (!local_using_sysemu)
>+	if (!local_using_sysptvm_or_sysemu)
> 	{
> 		err = ptrace(PTRACE_POKEUSR, pid, PT_SYSCALL_NR_OFFSET,
> 			     __NR_getpid);
>@@ -354,6 +354,7 @@
> 	int err, status, op, pid = userspace_pid[0];
> 	/* To prevent races if using_sysemu changes under us.*/
> 	int local_using_sysemu;
>+	int local_using_sysptvm;
> 
> 	if (getitimer(ITIMER_VIRTUAL, &timer))
> 		printk(UM_KERN_ERR "Failed to get itimer, errno = %d\n", errno);
>@@ -375,11 +376,12 @@
> 
> 		/* Now we set local_using_sysemu to be used for one loop */
> 		local_using_sysemu = get_using_sysemu();
>+		local_using_sysptvm = get_using_sysptvm();
> 
> 		op = SELECT_PTRACE_OPERATION(local_using_sysemu,
> 					     singlestepping(NULL));
> 
>-		if (ptrace(op, pid, 0, 0)) {
>+		if (ptrace(op, pid, local_using_sysptvm, 0)) {
> 			printk(UM_KERN_ERR "userspace - ptrace continue "
> 			       "failed, op = %d, errno = %d\n", op, errno);
> 			fatal_sigsegv();
>diff -Naur linux-2.6.29-rc7-git4/arch/um/os-Linux/start_up.c linux-2.6.29-rc7-git4.vm2/arch/um/os-Linux/start_up.c
>--- linux-2.6.29-rc7-git4/arch/um/os-Linux/start_up.c	2009-03-11 09:25:27.000000000 +0100
>+++ linux-2.6.29-rc7-git4.vm2/arch/um/os-Linux/start_up.c	2009-03-11 09:58:40.000000000 +0100
>@@ -198,6 +198,34 @@
> "    See http://perso.wanadoo.fr/laurent.vivier/UML/ for further \n"
> "    information.\n\n");
> 
>+/* Changed only during early boot */
>+static int force_sysptvm_disabled;
>+
>+static int __init nosysptvm_cmd_param(char *str, int* add)
>+{
>+	force_sysptvm_disabled = 1;
>+	return 0;
>+}
>+
>+__uml_setup("nosysptvm", nosysptvm_cmd_param,
>+"nosysptvm\n"
>+"    Turns off syscall emulation tags for ptrace (ptrace_vm) on.\n"
>+"    Ptrace_vm is a feature introduced by Renzo Davoli. It changes\n"
>+"    behaviour of ptrace() and helps reducing host context switch rate.\n\n");
>+
>+static int use_sysemu;
>+
>+static int __init usesysemu_cmd_param(char *str, int* add)

I don't like this function name either. :(

>+{
>+	use_sysemu = 1;
>+	return 0;
>+}
>+
>+__uml_setup("usesysemu", usesysemu_cmd_param,
>+"usesysemu\n"
>+"    Use sysemu instead of sysptvm even when the kernel supports it.\n\n"
>+);
>+
> static void __init check_sysemu(void)
> {
> 	unsigned long regs[MAX_REG_NR];
>@@ -293,6 +321,114 @@
> 	non_fatal("missing\n");
> }
> 
>+/*
>+ * test thread code. This thread is started only to test
>+ * which features are provided by the linux kernel
>+ */
>+static int sysptvm_child(void *arg)
>+{
>+	int *featurep = arg;
>+	int p[2] = {-1, -1};
>+	pid_t pid = os_getpid();
>+	if (ptrace(PTRACE_TRACEME, 0, 0, 0) < 0) {
>+		perror("ptrace test_ptracemulti");
>+		kill(pid, SIGKILL);
>+	}
>+	kill(pid, SIGSTOP);
>+	*featurep = 0;
>+	os_getpid();
>+	/*
>+	 * if it reaches this point in 1 stop it means that
>+	 * PTRACE_SYSCALL_SKIPEXIT works
>+	 */
>+	*featurep = PTRACE_SYSCALL_SKIPEXIT;
>+	pipe(p);
>+	/*
>+	 * if after a PTRACE_SYSCALL_SKIPCALL p[0] is already <0
>+	 * pipe has been really skipped
>+	 */
>+	if (p[0] < 0)
>+		*featurep = PTRACE_SYSCALL_SKIPCALL;
>+	else { /* clean up everything */
>+		close(p[0]);
>+		close(p[1]);
>+	}
>+	return 0;
>+}
>+
>+/*
>+ * kernel feature test:
>+ * it returns:
>+ *   -1 error
>+ *   0 old PTRACE_SYSCALL (addr is ignored)
>+ *   PTRACE_SYSCALL_SKIPEXIT: just skip_exit is provided
>+ *   PTRACE_SYSCALL_SKIPCALL: the entire syntax is implemented
>+ *   by the running kernel
>+ */
>+static int __init test_ptrace_sysptvm(void)

How about check_ptrace_sysptvm? Since it is consistent with
other check_XXX functions.

>+{
>+	int pid, status, rv, feature;
>+	static char stack[1024];
>+	feature = 0;
>+
>+	pid = clone(sysptvm_child, &stack[1020], SIGCHLD | CLONE_VM, &feature);
>+	if (pid < 0)
>+		return 0;
>+	if (waitpid(pid, &status, WUNTRACED) < 0) {
>+		kill(pid, SIGKILL);
>+		return 0;
>+	}
>+	/* restart and wait for the next syscall (getpid)*/
>+	rv = ptrace(PTRACE_SYSCALL, pid, 0, 0);
>+	if (waitpid(pid, &status, WUNTRACED) < 0)
>+		goto out;
>+	/* try to skip the exit call */
>+	rv = ptrace(PTRACE_SYSCALL, pid, PTRACE_SYSCALL_SKIPEXIT, 0);
>+	if (rv < 0)
>+		goto out;
>+	/* wait for the next stop */
>+	if (waitpid(pid, &status, WUNTRACED) < 0)
>+		goto out;
>+	/*
>+	 * if feature is already 0 it means that this is the exit call,
>+	 * and it has not been skipped, otherwise this is the
>+	 * entry call for the system call "time"
>+	 */
>+	if (feature < PTRACE_SYSCALL_SKIPEXIT)
>+		goto out;
>+	/* restart (time) and and try to skip the entire call */
>+	rv = ptrace(PTRACE_SYSCALL, pid, PTRACE_SYSCALL_SKIPCALL, 0);
>+	if (waitpid(pid, &status, WUNTRACED) < 0)
>+		return 0;
>+out:
>+	ptrace(PTRACE_KILL, pid, 0, 0);
>+	/* eliminate zombie */
>+	if (waitpid(pid, &status, WUNTRACED) < 0)
>+		return 0;
>+	return feature;
>+}
>+
>+static int  __init check_sysptvm(void)
>+{
>+	int feature = test_ptrace_sysptvm();
>+
>+	non_fatal("Checking ptrace new tags for syscall emulation...");
>+	if (feature == PTRACE_SYSCALL_SKIPCALL) {
>+		sysptvm_supported = 1;
>+		non_fatal("OK");
>+		if (!force_sysptvm_disabled) {
>+			set_using_sysptvm(PTRACE_SYSCALL_SKIPCALL);
>+			non_fatal("\n");
>+			return 1;
>+		} else {
>+			non_fatal(" (disabled)\n");
>+			return 0;
>+		}
>+	} else
>+		non_fatal("unsupported\n");
>+	return 0;
>+}
>+
> static void __init check_ptrace(void)
> {
> 	int pid, syscall, n, status;
>@@ -330,7 +466,8 @@
> 	}
> 	stop_ptraced_child(pid, 0, 1);
> 	non_fatal("OK\n");
>-	check_sysemu();
>+	if (use_sysemu || !check_sysptvm())
>+		check_sysemu();
> }
> 
> extern void check_tmpexec(void);

-- 
Do what you love, f**k the rest! F**k the regulations!
 

Re: [PATCH 2/2] ptrace_vm: ptrace for syscall emulation virtual machines

[Renzo Davoli]

Dear Cong,

Thank you for the detailed analysis of the code.
I'll change the code taking care of your observations asap.

On Mon, Mar 16, 2009 at 04:15:08PM +0800, Am??rico Wang wrote:
> >I have updated the patch, now it should be (more) consistent
> >with the Coding Style specifications.
> You can use scripts/checkpatch.pl to check it before sending.
I read the coding style document and I used the perl script.
However, the script is not able to cope with all the style specifications
and I may have missed something more. 
> 
> >UML tests at startup which features are provided and uses PTRACE_VM or
> >PTRACE_SYSEMU (or nothing). PTRACE_VM and/or PTRACE_SYSEMU support can be
> >disabled by command line flags.
> So what? PTRACE_VM is only supported in UML with this patch,
> UML still has to use PTRACE_SYSEMU on x86_32.
> 
> Am I missing something? :)
This patch [2/2] is for UML (host and guest). Patch #1 provides PTRACE_VM
for all the architectures supporting ptrace via tracehook.
By applying both patches PTRACE_VM is available in the following architectures:
x86*, sparc*, s390, powerpc*, ia64, sh* and um.
(I have not tested all these architectures, but the patch applies to the core ptrace
code, shared by all of them).
Ptrace_vm then provides the same speedup of PTRACE_SYSEMU extending its support:
- to other architectures: ports of UML or similar code for other architectures can
use it
- to other applications: PTRACE_SYSEMU supports the virtualization of all the system calls
while by PTRACE_VM the VM monitor can virtualize some of the system calls, depending on
some condition e.g. the value of a parameter. It is possible in this way give a faster
implementation to partial virtual machines like my umview.  

With patch #2 user-mode linux also uses ptrace_vm where available.

renzo

Re: [PATCH 2/2] ptrace_vm: ptrace for syscall emulation virtual machines

[Américo Wang]

On Mon, Mar 16, 2009 at 01:17:32PM +0100, Renzo Davoli wrote:
>Dear Cong,
>
>Thank you for the detailed analysis of the code.
>I'll change the code taking care of your observations asap.


You are so welcome. :)

>
>On Mon, Mar 16, 2009 at 04:15:08PM +0800, Am??rico Wang wrote:
>> >I have updated the patch, now it should be (more) consistent
>> >with the Coding Style specifications.
>> You can use scripts/checkpatch.pl to check it before sending.
>I read the coding style document and I used the perl script.
>However, the script is not able to cope with all the style specifications
>and I may have missed something more. 
>> 
>> >UML tests at startup which features are provided and uses PTRACE_VM or
>> >PTRACE_SYSEMU (or nothing). PTRACE_VM and/or PTRACE_SYSEMU support can be
>> >disabled by command line flags.
>> So what? PTRACE_VM is only supported in UML with this patch,
>> UML still has to use PTRACE_SYSEMU on x86_32.
>> 
>> Am I missing something? :)
>This patch [2/2] is for UML (host and guest). Patch #1 provides PTRACE_VM
>for all the architectures supporting ptrace via tracehook.
>By applying both patches PTRACE_VM is available in the following architectures:
>x86*, sparc*, s390, powerpc*, ia64, sh* and um.
>(I have not tested all these architectures, but the patch applies to the core ptrace
>code, shared by all of them).

Ok then. I am not familiar with tracehooks.

>Ptrace_vm then provides the same speedup of PTRACE_SYSEMU extending its support:
>- to other architectures: ports of UML or similar code for other architectures can
>use it
>- to other applications: PTRACE_SYSEMU supports the virtualization of all the system calls
>while by PTRACE_VM the VM monitor can virtualize some of the system calls, depending on
>some condition e.g. the value of a parameter. It is possible in this way give a faster
>implementation to partial virtual machines like my umview.  
>
>With patch #2 user-mode linux also uses ptrace_vm where available.
>

Thanks for your explanations!

-- 
Do what you love, f**k the rest! F**k the regulations!
 

Re: [PATCH 2/2] ptrace_vm: ptrace for syscall emulation virtual machines

[Renzo Davoli]

Patch rebased on 2.6.29. I have fixed the code following Cong's suggestion.
	renzo
Although get_using_sysptvm is used as a boolean, I have left it int just 
for the sake of simmetry with get_using_sysemu.
It could be safely changed to boolean at any time.

Signed-off-by: Renzo Davoli <renzo@cs.unibo.it>
---
diff -Naur linux-2.6.29-vm/arch/um/include/shared/kern_util.h linux-2.6.29-vm2/arch/um/include/shared/kern_util.h
--- linux-2.6.29-vm/arch/um/include/shared/kern_util.h	2009-03-24 22:04:09.000000000 +0100
+++ linux-2.6.29-vm2/arch/um/include/shared/kern_util.h	2009-03-24 22:12:50.000000000 +0100
@@ -57,7 +57,7 @@
 extern unsigned long to_irq_stack(unsigned long *mask_out);
 extern unsigned long from_irq_stack(int nested);
 
-extern void syscall_trace(struct uml_pt_regs *regs, int entryexit);
+extern int syscall_trace(struct uml_pt_regs *regs, int entryexit);
 extern int singlestepping(void *t);
 
 extern void segv_handler(int sig, struct uml_pt_regs *regs);
diff -Naur linux-2.6.29-vm/arch/um/include/shared/ptrace_user.h linux-2.6.29-vm2/arch/um/include/shared/ptrace_user.h
--- linux-2.6.29-vm/arch/um/include/shared/ptrace_user.h	2009-03-24 22:04:09.000000000 +0100
+++ linux-2.6.29-vm2/arch/um/include/shared/ptrace_user.h	2009-03-24 22:12:50.000000000 +0100
@@ -40,9 +40,20 @@
 #define PTRACE_OLDSETOPTIONS PTRACE_SETOPTIONS
 #endif
 
+/* these constant should eventually enter in sys/ptrace.h */
+#ifndef PTRACE_SYSCALL_SKIPCALL
+#define PTRACE_SYSCALL_SKIPCALL      0x6
+#endif
+#ifndef PTRACE_SYSCALL_SKIPEXIT
+#define PTRACE_SYSCALL_SKIPEXIT      0x2
+#endif
+
 void set_using_sysemu(int value);
 int get_using_sysemu(void);
 extern int sysemu_supported;
+void set_using_sysptvm(int value);
+int get_using_sysptvm(void);
+extern int sysptvm_supported;
 
 #define SELECT_PTRACE_OPERATION(sysemu_mode, singlestep_mode) \
 	(((int[3][3] ) { \
diff -Naur linux-2.6.29-vm/arch/um/kernel/process.c linux-2.6.29-vm2/arch/um/kernel/process.c
--- linux-2.6.29-vm/arch/um/kernel/process.c	2009-03-24 22:04:09.000000000 +0100
+++ linux-2.6.29-vm2/arch/um/kernel/process.c	2009-03-24 22:12:50.000000000 +0100
@@ -322,7 +322,9 @@
 }
 
 static atomic_t using_sysemu = ATOMIC_INIT(0);
+static atomic_t using_sysptvm = ATOMIC_INIT(0);
 int sysemu_supported;
+int sysptvm_supported;
 
 void set_using_sysemu(int value)
 {
@@ -336,7 +338,18 @@
 	return atomic_read(&using_sysemu);
 }
 
-static int proc_read_sysemu(char *buf, char **start, off_t offset, int size,int *eof, void *data)
+void set_using_sysptvm(int value)
+{
+	atomic_set(&using_sysptvm, value);
+}
+
+int get_using_sysptvm(void)
+{
+	return atomic_read(&using_sysptvm);
+}
+
+static int proc_read_sysemu(char *buf, char **start, off_t offset,
+		int size, int *eof, void *data)
 {
 	if (snprintf(buf, size, "%d\n", get_using_sysemu()) < size)
 		/* No overflow */
@@ -345,7 +358,8 @@
 	return strlen(buf);
 }
 
-static int proc_write_sysemu(struct file *file,const char __user *buf, unsigned long count,void *data)
+static int proc_write_sysemu(struct file *file, const char __user *buf,
+		unsigned long count, void *data)
 {
 	char tmp[2];
 
@@ -358,27 +372,63 @@
 	return count;
 }
 
-int __init make_proc_sysemu(void)
+
+static int proc_read_sysptvm(char *buf, char **start, off_t offset,
+		int size, int *eof, void *data)
 {
-	struct proc_dir_entry *ent;
-	if (!sysemu_supported)
-		return 0;
+	int sysptvm = (get_using_sysptvm() != 0);
+	if (snprintf(buf, size, "%d\n", sysptvm) < size)
+		/* No overflow */
+		*eof = 1;
 
-	ent = create_proc_entry("sysemu", 0600, NULL);
+	return strlen(buf);
+}
 
-	if (ent == NULL)
-	{
-		printk(KERN_WARNING "Failed to register /proc/sysemu\n");
-		return 0;
-	}
+static int proc_write_sysptvm(struct file *file, const char __user *buf,
+		unsigned long count, void *data)
+{
+	char tmp[2];
+
+	if (copy_from_user(tmp, buf, 1))
+		return -EFAULT;
+
+	if (tmp[0] == '0')
+		set_using_sysptvm(0);
+	if (tmp[0] == '1')
+		set_using_sysemu(/* XXX */ 6);
+	/* We use the first char, but pretend to write everything */
+	return count;
+}
 
-	ent->read_proc  = proc_read_sysemu;
-	ent->write_proc = proc_write_sysemu;
+int __init make_proc_sysemu_or_sysptvm(void)
+{
+	struct proc_dir_entry *ent;
 
+	if (sysptvm_supported) {
+		ent = create_proc_entry("sysptvm", 0600, NULL);
+
+		if (ent == NULL) {
+			printk(KERN_WARNING "Failed to register /proc/sysptvm\n");
+			return 0;
+		}
+
+		ent->read_proc  = proc_read_sysptvm;
+		ent->write_proc = proc_write_sysptvm;
+	} else if (sysemu_supported) {
+		ent = create_proc_entry("sysemu", 0600, NULL);
+
+		if (ent == NULL) {
+			printk(KERN_WARNING "Failed to register /proc/sysemu\n");
+			return 0;
+		}
+
+		ent->read_proc  = proc_read_sysemu;
+		ent->write_proc = proc_write_sysemu;
+	}
 	return 0;
 }
 
-late_initcall(make_proc_sysemu);
+late_initcall(make_proc_sysemu_or_sysptvm);
 
 int singlestepping(void * t)
 {
diff -Naur linux-2.6.29-vm/arch/um/kernel/ptrace.c linux-2.6.29-vm2/arch/um/kernel/ptrace.c
--- linux-2.6.29-vm/arch/um/kernel/ptrace.c	2009-03-24 22:04:09.000000000 +0100
+++ linux-2.6.29-vm2/arch/um/kernel/ptrace.c	2009-03-24 22:14:51.000000000 +0100
@@ -81,6 +81,8 @@
 		if (request == PTRACE_SYSCALL)
 			set_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 		else clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
+		child->ptrace &= ~PT_SYSCALL_MASK;
+		child->ptrace |= PTRACE2PT_SYSCALL(addr);
 		child->exit_code = data;
 		wake_up_process(child);
 		ret = 0;
@@ -107,7 +109,9 @@
 		ret = -EIO;
 		if (!valid_signal(data))
 			break;
+		child->ptrace &= ~PT_SYSCALL_MASK;
 		clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
+		child->ptrace |= (addr & PTRACE_SYSCALL_MASK) << 28;
 		set_singlestepping(child, 1);
 		child->exit_code = data;
 		/* give it a chance to run. */
@@ -250,7 +254,7 @@
  * XXX Check PT_DTRACE vs TIF_SINGLESTEP for singlestepping check and
  * PT_PTRACED vs TIF_SYSCALL_TRACE for syscall tracing check
  */
-void syscall_trace(struct uml_pt_regs *regs, int entryexit)
+int syscall_trace(struct uml_pt_regs *regs, int entryexit)
 {
 	int is_singlestep = (current->ptrace & PT_DTRACE) && entryexit;
 	int tracesysgood;
@@ -272,10 +276,13 @@
 		send_sigtrap(current, regs, 0);
 
 	if (!test_thread_flag(TIF_SYSCALL_TRACE))
-		return;
+		return 0;
 
 	if (!(current->ptrace & PT_PTRACED))
-		return;
+		return 0;
+
+	if (entryexit && (current->ptrace & PT_SYSCALL_SKIPEXIT))
+		return 0;
 
 	/*
 	 * the 0x80 provides a way for the tracing parent to distinguish
@@ -296,4 +303,8 @@
 		send_sig(current->exit_code, current, 1);
 		current->exit_code = 0;
 	}
+	if (!entryexit && (current->ptrace & PT_SYSCALL_SKIPCALL))
+		return 1;
+	else
+		return 0;
 }
diff -Naur linux-2.6.29-vm/arch/um/kernel/skas/syscall.c linux-2.6.29-vm2/arch/um/kernel/skas/syscall.c
--- linux-2.6.29-vm/arch/um/kernel/skas/syscall.c	2009-03-24 22:04:09.000000000 +0100
+++ linux-2.6.29-vm2/arch/um/kernel/skas/syscall.c	2009-03-24 22:12:50.000000000 +0100
@@ -17,8 +17,9 @@
 	struct pt_regs *regs = container_of(r, struct pt_regs, regs);
 	long result;
 	int syscall;
+	int skip_call;
 
-	syscall_trace(r, 0);
+	skip_call = syscall_trace(r, 0);
 
 	/*
 	 * This should go in the declaration of syscall, but when I do that,
@@ -29,12 +30,15 @@
 	 *     gcc version 4.0.1 20050727 (Red Hat 4.0.1-5)
 	 * in case it's a compiler bug.
 	 */
-	syscall = UPT_SYSCALL_NR(r);
-	if ((syscall >= NR_syscalls) || (syscall < 0))
-		result = -ENOSYS;
-	else result = EXECUTE_SYSCALL(syscall, regs);
+	if (skip_call == 0) {
+		syscall = UPT_SYSCALL_NR(r);
+		if ((syscall >= NR_syscalls) || (syscall < 0))
+			result = -ENOSYS;
+		else
+			result = EXECUTE_SYSCALL(syscall, regs);
 
-	REGS_SET_SYSCALL_RETURN(r->gp, result);
+		REGS_SET_SYSCALL_RETURN(r->gp, result);
+	}
 
 	syscall_trace(r, 1);
 }
diff -Naur linux-2.6.29-vm/arch/um/os-Linux/skas/process.c linux-2.6.29-vm2/arch/um/os-Linux/skas/process.c
--- linux-2.6.29-vm/arch/um/os-Linux/skas/process.c	2009-03-24 22:04:09.000000000 +0100
+++ linux-2.6.29-vm2/arch/um/os-Linux/skas/process.c	2009-03-24 22:24:07.000000000 +0100
@@ -153,11 +153,11 @@
 }
 
 /*
- * To use the same value of using_sysemu as the caller, ask it that value
- * (in local_using_sysemu
+ * To use the same value of using_sysptvm or using_sysemu as the caller, i
+ * ask it that value in use_sys_ptvm_or_emu
  */
 static void handle_trap(int pid, struct uml_pt_regs *regs,
-			int local_using_sysemu)
+			int use_sys_ptvm_or_emu)
 {
 	int err, status;
 
@@ -167,7 +167,7 @@
 	/* Mark this as a syscall */
 	UPT_SYSCALL_NR(regs) = PT_SYSCALL_NR(regs->gp);
 
-	if (!local_using_sysemu)
+	if (!use_sys_ptvm_or_emu)
 	{
 		err = ptrace(PTRACE_POKEUSR, pid, PT_SYSCALL_NR_OFFSET,
 			     __NR_getpid);
@@ -354,6 +354,7 @@
 	int err, status, op, pid = userspace_pid[0];
 	/* To prevent races if using_sysemu changes under us.*/
 	int local_using_sysemu;
+	int local_using_sysptvm;
 
 	if (getitimer(ITIMER_VIRTUAL, &timer))
 		printk(UM_KERN_ERR "Failed to get itimer, errno = %d\n", errno);
@@ -375,11 +376,12 @@
 
 		/* Now we set local_using_sysemu to be used for one loop */
 		local_using_sysemu = get_using_sysemu();
+		local_using_sysptvm = get_using_sysptvm();
 
 		op = SELECT_PTRACE_OPERATION(local_using_sysemu,
 					     singlestepping(NULL));
 
-		if (ptrace(op, pid, 0, 0)) {
+		if (ptrace(op, pid, local_using_sysptvm, 0)) {
 			printk(UM_KERN_ERR "userspace - ptrace continue "
 			       "failed, op = %d, errno = %d\n", op, errno);
 			fatal_sigsegv();
diff -Naur linux-2.6.29-vm/arch/um/os-Linux/start_up.c linux-2.6.29-vm2/arch/um/os-Linux/start_up.c
--- linux-2.6.29-vm/arch/um/os-Linux/start_up.c	2009-03-24 22:04:09.000000000 +0100
+++ linux-2.6.29-vm2/arch/um/os-Linux/start_up.c	2009-03-24 22:12:50.000000000 +0100
@@ -198,6 +198,34 @@
 "    See http://perso.wanadoo.fr/laurent.vivier/UML/ for further \n"
 "    information.\n\n");
 
+/* Changed only during early boot */
+static int force_sysptvm_disabled;
+
+static int __init nosysptvm_cmd_param(char *str, int* add)
+{
+	force_sysptvm_disabled = 1;
+	return 0;
+}
+
+__uml_setup("nosysptvm", nosysptvm_cmd_param,
+"nosysptvm\n"
+"    Turns off syscall emulation tags for ptrace (ptrace_vm) on.\n"
+"    Ptrace_vm is a feature introduced by Renzo Davoli. It changes\n"
+"    behaviour of ptrace() and helps reducing host context switch rate.\n\n");
+
+static int use_sysemu;
+
+static int __init usesysemu_cmd_param(char *str, int* add)
+{
+	use_sysemu = 1;
+	return 0;
+}
+
+__uml_setup("usesysemu", usesysemu_cmd_param,
+"usesysemu\n"
+"    Use sysemu instead of sysptvm even when the kernel supports it.\n\n"
+);
+
 static void __init check_sysemu(void)
 {
 	unsigned long regs[MAX_REG_NR];
@@ -293,6 +321,114 @@
 	non_fatal("missing\n");
 }
 
+/*
+ * test thread code. This thread is started only to test
+ * which features are provided by the linux kernel
+ */
+static int sysptvm_child(void *arg)
+{
+	int *featurep = arg;
+	int p[2] = {-1, -1};
+	pid_t pid = os_getpid();
+	if (ptrace(PTRACE_TRACEME, 0, 0, 0) < 0) {
+		perror("ptrace test_ptracemulti");
+		kill(pid, SIGKILL);
+	}
+	kill(pid, SIGSTOP);
+	*featurep = 0;
+	os_getpid();
+	/*
+	 * if it reaches this point in 1 stop it means that
+	 * PTRACE_SYSCALL_SKIPEXIT works
+	 */
+	*featurep = PTRACE_SYSCALL_SKIPEXIT;
+	pipe(p);
+	/*
+	 * if after a PTRACE_SYSCALL_SKIPCALL p[0] is already <0
+	 * pipe has been really skipped
+	 */
+	if (p[0] < 0)
+		*featurep = PTRACE_SYSCALL_SKIPCALL;
+	else { /* clean up everything */
+		close(p[0]);
+		close(p[1]);
+	}
+	return 0;
+}
+
+/*
+ * kernel feature test:
+ * it returns:
+ *   -1 error
+ *   0 old PTRACE_SYSCALL (addr is ignored)
+ *   PTRACE_SYSCALL_SKIPEXIT: just skip_exit is provided
+ *   PTRACE_SYSCALL_SKIPCALL: the entire syntax is implemented
+ *   by the running kernel
+ */
+static int __init test_ptrace_sysptvm(void)
+{
+	int pid, status, rv, feature;
+	static char stack[1024];
+	feature = 0;
+
+	pid = clone(sysptvm_child, &stack[1020], SIGCHLD | CLONE_VM, &feature);
+	if (pid < 0)
+		return 0;
+	if (waitpid(pid, &status, WUNTRACED) < 0) {
+		kill(pid, SIGKILL);
+		return 0;
+	}
+	/* restart and wait for the next syscall (getpid)*/
+	rv = ptrace(PTRACE_SYSCALL, pid, 0, 0);
+	if (waitpid(pid, &status, WUNTRACED) < 0)
+		goto out;
+	/* try to skip the exit call */
+	rv = ptrace(PTRACE_SYSCALL, pid, PTRACE_SYSCALL_SKIPEXIT, 0);
+	if (rv < 0)
+		goto out;
+	/* wait for the next stop */
+	if (waitpid(pid, &status, WUNTRACED) < 0)
+		goto out;
+	/*
+	 * if feature is already 0 it means that this is the exit call,
+	 * and it has not been skipped, otherwise this is the
+	 * entry call for the system call "time"
+	 */
+	if (feature < PTRACE_SYSCALL_SKIPEXIT)
+		goto out;
+	/* restart (time) and and try to skip the entire call */
+	rv = ptrace(PTRACE_SYSCALL, pid, PTRACE_SYSCALL_SKIPCALL, 0);
+	if (waitpid(pid, &status, WUNTRACED) < 0)
+		return 0;
+out:
+	ptrace(PTRACE_KILL, pid, 0, 0);
+	/* eliminate zombie */
+	if (waitpid(pid, &status, WUNTRACED) < 0)
+		return 0;
+	return feature;
+}
+
+static int  __init check_sysptvm(void)
+{
+	int feature = test_ptrace_sysptvm();
+
+	non_fatal("Checking ptrace new tags for syscall emulation...");
+	if (feature == PTRACE_SYSCALL_SKIPCALL) {
+		sysptvm_supported = 1;
+		non_fatal("OK");
+		if (!force_sysptvm_disabled) {
+			set_using_sysptvm(PTRACE_SYSCALL_SKIPCALL);
+			non_fatal("\n");
+			return 1;
+		} else {
+			non_fatal(" (disabled)\n");
+			return 0;
+		}
+	} else
+		non_fatal("unsupported\n");
+	return 0;
+}
+
 static void __init check_ptrace(void)
 {
 	int pid, syscall, n, status;
@@ -330,7 +466,8 @@
 	}
 	stop_ptraced_child(pid, 0, 1);
 	non_fatal("OK\n");
-	check_sysemu();
+	if (use_sysemu || !check_sysptvm())
+		check_sysemu();
 }
 
 extern void check_tmpexec(void);

Re: [PATCH 2/2] ptrace_vm: ptrace for syscall emulation virtual machines

[Américo Wang]

On Wed, Mar 25, 2009 at 12:20:19AM +0100, Renzo Davoli wrote:
>Patch rebased on 2.6.29. I have fixed the code following Cong's suggestion.
>	renzo
>Although get_using_sysptvm is used as a boolean, I have left it int just 
>for the sake of simmetry with get_using_sysemu.
>It could be safely changed to boolean at any time.
>

Thanks.

My point is *not* changing it from 'int' to 'bool', I mean you
should change the interface, for example, change get_using_sysptvm()
to enable_sysptvm().