Message-ID: <48f8a9d6.05a0660a.7460.77d4@mx.google.com>
Date:	Fri, 17 Oct 2008 08:05:58 -0700 (PDT)
From:	eranian@...glemail.com
To:	linux-kernel@...r.kernel.org
Subject: [patch 20/24] perfmon3:  system calls interface

This patch adds the top level perfmon system calls.

Signed-off-by: Stephane Eranian <eranian@...il.com>
--

Index: o3/perfmon/perfmon_syscalls.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ o3/perfmon/perfmon_syscalls.c	2008-10-16 11:51:36.000000000 +0200
@@ -0,0 +1,741 @@
+/*
+ * perfmon_syscalls.c: perfmon2 system call interface
+ *
+ * This file implements the perfmon2 interface which
+ * provides access to the hardware performance counters
+ * of the host processor.
+ *
+ * The initial version of perfmon.c was written by
+ * Ganesh Venkitachalam, IBM Corp.
+ *
+ * Then it was modified for perfmon-1.x by Stephane Eranian and
+ * David Mosberger, Hewlett Packard Co.
+ *
+ * Version Perfmon-2.x is a complete rewrite of perfmon-1.x
+ * by Stephane Eranian, Hewlett Packard Co.
+ *
+ * Copyright (c) 1999-2006 Hewlett-Packard Development Company, L.P.
+ * Contributed by Stephane Eranian <eranian@....hp.com>
+ *                David Mosberger-Tang <davidm@....hp.com>
+ *
+ * More information about perfmon available at:
+ * 	http://perfmon2.sf.net
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+ * 02111-1307 USA
+ */
+#include <linux/kernel.h>
+#include <linux/fs.h>
+#include <linux/ptrace.h>
+#include <linux/perfmon_kern.h>
+#include <linux/uaccess.h>
+#include "perfmon_priv.h"
+
+/*
+ * Context locking rules:
+ * ---------------------
+ * 	- any thread with access to the file descriptor of a context can
+ * 	  potentially issue perfmon calls
+ *
+ * 	- calls must be serialized to guarantee correctness
+ *
+ * 	- as soon as a context is attached to a thread or CPU, it may be
+ * 	  actively monitoring. On some architectures, such as IA-64, this
+ * 	  is true even though the pfm_start() call has not been made. This
+ * 	  comes from the fact that on some architectures, it is possible to
+ * 	  start/stop monitoring from userland.
+ *
+ *	- If monitoring is active, then there can PMU interrupts. Because
+ *	  context accesses must be serialized, the perfmon system calls
+ *	  must mask interrupts as soon as the context is attached.
+ *
+ *	- perfmon system calls that operate with the context unloaded cannot
+ *	  assume it is actually unloaded when they are called. They first need
+ *	  to check and for that they need interrupts masked. Then, if the
+ *	  context is actually unloaded, they can unmask interrupts.
+ *
+ *	- interrupt masking holds true for other internal perfmon functions as
+ *	  well. Except for PMU interrupt handler because those interrupts
+ *	  cannot be nested.
+ *
+ * 	- we mask ALL interrupts instead of just the PMU interrupt because we
+ * 	  also need to protect against timer interrupts which could trigger
+ * 	  a set switch.
+ */
+
+struct pfm_syscall_cookie {
+	struct file *filp;
+	int fput_needed;
+};
+
+/*
+ * cannot attach if :
+ * 	- kernel task
+ * 	- task not owned by caller (checked by ptrace_may_attach())
+ * 	- task is dead or zombie
+ * 	- cannot use blocking notification when self-monitoring
+ */
+static int pfm_task_incompatible(struct pfm_context *ctx,
+				 struct task_struct *task)
+{
+	/*
+	 * cannot attach to a kernel thread
+	 */
+	if (!task->mm) {
+		PFM_DBG("cannot attach to kernel thread [%d]", task->pid);
+		return -EPERM;
+	}
+
+	/*
+	 * cannot attach to a zombie task
+	 */
+	if (task->exit_state == EXIT_ZOMBIE || task->exit_state == EXIT_DEAD) {
+		PFM_DBG("cannot attach to zombie/dead task [%d]", task->pid);
+		return -EBUSY;
+	}
+	return 0;
+}
+
+/**
+ * pfm_get_task -- check permission and acquire task to monitor
+ * @ctx: perfmon context
+ * @pid: identification of the task to check
+ * @task: upon return, a pointer to the task to monitor
+ *
+ * This function  is used in per-thread mode only AND when not
+ * self-monitoring. It finds the task to monitor and checks
+ * that the caller has permissions to attach. It also checks
+ * that the task is stopped via ptrace so that we can safely
+ * modify its state.
+ *
+ * task refcount is incremented when succesful.
+ */
+static int pfm_get_task(struct pfm_context *ctx, pid_t pid,
+			struct task_struct **task)
+{
+	struct task_struct *p;
+	int ret = 0, ret1 = 0;
+
+	/*
+	 * When attaching to another thread we must ensure
+	 * that the thread is actually stopped. Just like with
+	 * perfmon system calls, we enforce that the thread
+	 * be ptraced and STOPPED by using ptrace_check_attach().
+	 *
+	 * As a consequence, only the ptracing parent can actually
+	 * attach a context to a thread. Obviously, this constraint
+	 * does not exist for self-monitoring threads.
+	 *
+	 * We use ptrace_may_access() to check for permission.
+	 */
+	read_lock(&tasklist_lock);
+
+	p = find_task_by_vpid(pid);
+	if (p)
+		get_task_struct(p);
+
+	read_unlock(&tasklist_lock);
+
+	if (!p) {
+		PFM_DBG("task not found %d", pid);
+		return -ESRCH;
+	}
+
+	ret = -EPERM;
+
+	/*
+	 * returns 0 if cannot attach
+	 */
+	ret1 = ptrace_may_access(p, PTRACE_MODE_ATTACH);
+	if (ret1)
+		ret = ptrace_check_attach(p, 0);
+
+	PFM_DBG("may_attach=%d check_attach=%d", ret1, ret);
+
+	if (ret || !ret1)
+		goto error;
+
+	ret = pfm_task_incompatible(ctx, p);
+	if (ret)
+		goto error;
+
+	*task = p;
+
+	return 0;
+error:
+	if (!(ret1 || ret))
+		ret = -EPERM;
+
+	put_task_struct(p);
+
+	return ret;
+}
+
+/*
+ * context must be locked when calling this function
+ */
+int __pfm_check_task_state(struct pfm_context *ctx, int check_mask,
+			 unsigned long *flags)
+{
+	struct task_struct *task;
+	unsigned long local_flags, new_flags;
+	int state, ret;
+
+recheck:
+	/*
+	 * task is NULL for system-wide context
+	 */
+	task = ctx->task;
+	state = ctx->state;
+	local_flags = *flags;
+
+	PFM_DBG("state=%d check_mask=0x%x task=[%d]",
+		state, check_mask, task ? task->pid:-1);
+	/*
+	 * if the context is detached, then we do not touch
+	 * hardware, therefore there is not restriction on when we can
+	 * access it.
+	 */
+	if (state == PFM_CTX_UNLOADED)
+		return 0;
+	/*
+	 * no command can operate on a zombie context.
+	 * A context becomes zombie when the file that identifies
+	 * it is closed while the context is still attached to the
+	 * thread it monitors.
+	 */
+	if (state == PFM_CTX_ZOMBIE)
+		return -EINVAL;
+
+	/*
+	 * at this point, state is PFM_CTX_LOADED
+	 */
+
+	/*
+	 * some commands require the context to be unloaded to operate
+	 */
+	if (check_mask & PFM_CMD_UNLOADED)  {
+		PFM_DBG("state=%d, cmd needs context unloaded", state);
+		return -EBUSY;
+	}
+
+	/*
+	 * self-monitoring always ok.
+	 */
+	if (task == current)
+		return 0;
+
+	/*
+	 * at this point, monitoring another thread
+	 */
+
+	/*
+	 * When we operate on another thread, we must wait for it to be
+	 * stopped and completely off any CPU as we need to access the
+	 * PMU state (or machine state).
+	 *
+	 * A thread can be put in the STOPPED state in various ways
+	 * including PTRACE_ATTACH, or when it receives a SIGSTOP signal.
+	 * We enforce that the thread must be ptraced, so it is stopped
+	 * AND it CANNOT wake up while we operate on it because this
+	 * would require an action from the ptracing parent which is the
+	 * thread that is calling this function.
+	 *
+	 * The dependency on ptrace, imposes that only the ptracing
+	 * parent can issue command on a thread. This is unfortunate
+	 * but we do not know of a better way of doing this.
+	 */
+	if (check_mask & PFM_CMD_STOPPED) {
+
+		spin_unlock_irqrestore(&ctx->lock, local_flags);
+
+		/*
+		 * check that the thread is ptraced AND STOPPED
+		 */
+		ret = ptrace_check_attach(task, 0);
+
+		spin_lock_irqsave(&ctx->lock, new_flags);
+
+		/*
+		 * flags may be different than when we released the lock
+		 */
+		*flags = new_flags;
+
+		if (ret)
+			return ret;
+		/*
+		 * we must recheck to verify if state has changed
+		 */
+		if (unlikely(ctx->state != state)) {
+			PFM_DBG("old_state=%d new_state=%d",
+				state,
+				ctx->state);
+			goto recheck;
+		}
+	}
+	return 0;
+}
+
+int pfm_check_task_state(struct pfm_context *ctx, int check_mask,
+			 unsigned long *flags)
+{
+	int ret;
+	ret  = __pfm_check_task_state(ctx, check_mask, flags);
+	PFM_DBG("ret=%d",ret);
+	return ret;
+}
+
+/**
+ * pfm_get_args - Function used to copy the syscall argument into kernel memory
+ * @ureq: user argument
+ * @sz: user argument size
+ * @lsz: size of stack buffer
+ * @laddr: stack buffer address
+ * @req: point to start of kernel copy of the argument
+ * @ptr_free: address of kernel copy to free
+ *
+ * There are two options:
+ * 	- use a stack buffer described by laddr (addresses) and lsz (size)
+ * 	- allocate memory
+ *
+ * return:
+ * 	< 0 : in case of error (ptr_free may not be updated)
+ * 	  0 : success
+ *      - req: points to base of kernel copy of arguments
+ *	- ptr_free: address of buffer to free by caller on exit.
+ *		    NULL if using the stack buffer
+ *
+ * when ptr_free is not NULL upon return, the caller must kfree()
+ */
+int pfm_get_args(void __user *ureq, size_t sz, size_t lsz, void *laddr,
+		 void **req, void **ptr_free)
+{
+	void *addr;
+
+	/*
+	 * check syadmin argument limit
+	 */
+	if (unlikely(sz > pfm_controls.arg_mem_max)) {
+		PFM_DBG("argument too big %zu max=%zu",
+			sz,
+			pfm_controls.arg_mem_max);
+		return -E2BIG;
+	}
+
+	/*
+	 * check if vector fits on stack buffer
+	 */
+	if (sz > lsz) {
+		addr = kmalloc(sz, GFP_KERNEL);
+		if (unlikely(addr == NULL))
+			return -ENOMEM;
+		*ptr_free = addr;
+	} else {
+		addr = laddr;
+		*req = laddr;
+		*ptr_free = NULL;
+	}
+
+	/*
+	 * bring the data in
+	 */
+	if (unlikely(copy_from_user(addr, ureq, sz))) {
+		if (addr != laddr)
+			kfree(addr);
+		return -EFAULT;
+	}
+
+	/*
+	 * base address of kernel buffer
+	 */
+	*req = addr;
+
+	return 0;
+}
+
+/**
+ * pfm_acquire_ctx_from_fd -- get ctx from file descriptor
+ * @fd: file descriptor
+ * @ctx: pointer to pointer of context updated on return
+ * @cookie: opaque structure to use for release
+ *
+ * This helper function extracts the ctx from the file descriptor.
+ * It also increments the refcount of the file structure. Thus
+ * it updates the cookie so the refcount can be decreased when
+ * leaving the perfmon syscall via pfm_release_ctx_from_fd
+ */
+static int pfm_acquire_ctx_from_fd(int fd, struct pfm_context **ctx,
+				   struct pfm_syscall_cookie *cookie)
+{
+	struct file *filp;
+	int fput_needed;
+
+	filp = fget_light(fd, &fput_needed);
+	if (unlikely(filp == NULL)) {
+		PFM_DBG("invalid fd %d", fd);
+		return -EBADF;
+	}
+
+	*ctx = filp->private_data;
+
+	if (unlikely(!*ctx || filp->f_op != &pfm_file_ops)) {
+		PFM_DBG("fd %d not related to perfmon", fd);
+		return -EBADF;
+	}
+	cookie->filp = filp;
+	cookie->fput_needed = fput_needed;
+
+	return 0;
+}
+
+/**
+ * pfm_release_ctx_from_fd -- decrease refcount of file associated with context
+ * @cookie: the cookie structure initialized by pfm_acquire_ctx_from_fd
+ */
+static inline void pfm_release_ctx_from_fd(struct pfm_syscall_cookie *cookie)
+{
+	fput_light(cookie->filp, cookie->fput_needed);
+}
+
+/**
+ * pfm_validate_type_sz -- validate sz based on type
+ * @type : PFM_RW_XX type passed to pfm_write or pfm_read
+ * @sz   : vector size in bytes
+ *
+ * return:
+ *    the number of elements in the vector, 0 if error
+ */
+static size_t pfm_validate_type_sz(int type, size_t sz)
+{
+	size_t count, sz_type;
+
+	switch(type) {
+	case PFM_RW_PMD:
+	case PFM_RW_PMC:
+		sz_type = sizeof(struct pfarg_pmr);
+		break;
+	default:
+		PFM_DBG("invalid type=%d", type);
+		return 0;
+	}
+
+	count = sz / sz_type;
+
+	if ((count * sz_type) != sz) {
+		PFM_DBG("invalid size=%zu for type=%d", sz, type);
+		return 0;
+	}
+
+	PFM_DBG("sz=%zu sz_type=%zu count=%zu",
+		sz,
+		sz_type,
+		count);
+
+	return count;
+}
+
+/*
+ * unlike the other perfmon system calls, this one returns a file descriptor
+ * or a value < 0 in case of error, very much like open() or socket()
+ */
+asmlinkage long sys_pfm_create(int flags, struct pfarg_sinfo __user *ureq)
+{
+	struct pfm_context *new_ctx;
+	struct pfarg_sinfo sif;
+	int ret;
+
+	PFM_DBG("flags=0x%x sif=%p", flags, ureq);
+
+	if (perfmon_disabled)
+		return -ENOSYS;
+
+	if (flags) {
+		PFM_DBG("no flags accepted yet");
+		return -EINVAL;
+	}
+	ret = __pfm_create_context(flags, &sif, &new_ctx);
+
+	/*
+	 * copy sif to user level argument, if requested
+	 */
+	if (ureq && copy_to_user(ureq, &sif, sizeof(sif))) {
+		pfm_undo_create(ret, new_ctx);
+		ret  = -EFAULT;
+	}
+	return ret;
+}
+
+asmlinkage long sys_pfm_write(int fd, int uflags,
+			      int type,
+			      void __user *ureq,
+			      size_t sz)
+{
+	u64 buf[PFM_STK_ARG];
+	struct pfm_context *ctx;
+	struct pfm_syscall_cookie cookie;
+	void *req, *fptr;
+	unsigned long flags;
+	size_t count;
+	int ret;
+
+	PFM_DBG("fd=%d flags=0x%x type=%d req=%p sz=%zu",
+		fd, uflags, type, ureq, sz);
+
+	if (uflags) {
+		PFM_DBG("no flags defined");
+		return -EINVAL;
+	}
+
+	count = pfm_validate_type_sz(type, sz);
+	if (!count)
+		return -EINVAL;
+
+	ret = pfm_acquire_ctx_from_fd(fd, &ctx, &cookie);
+	if (ret)
+		return ret;
+
+	ret = pfm_get_args(ureq, sz, sizeof(buf), buf, (void **)&req, &fptr);
+	if (ret)
+		goto error;
+
+	spin_lock_irqsave(&ctx->lock, flags);
+
+	ret = pfm_check_task_state(ctx, PFM_CMD_STOPPED, &flags);
+	if (ret)
+		goto skip;
+	switch(type) {
+	case PFM_RW_PMC:
+		ret = __pfm_write_pmcs(ctx, req, count);
+		break;
+	case PFM_RW_PMD:
+		ret = __pfm_write_pmds(ctx, req, count);
+		break;
+	default:
+		PFM_DBG("invalid type=%d", type);
+		ret = -EINVAL;
+	}
+skip:
+	spin_unlock_irqrestore(&ctx->lock, flags);
+
+	/*
+	 * This function may be on the critical path.
+	 * We want to avoid the branch if unecessary.
+	 */
+	if (fptr)
+		kfree(fptr);
+error:
+	pfm_release_ctx_from_fd(&cookie);
+	return ret;
+}
+
+asmlinkage long sys_pfm_read(int fd, int uflags,
+			     int type,
+			     void __user *ureq,
+			     size_t sz)
+{
+	u64 buf[PFM_STK_ARG];
+	struct pfm_context *ctx;
+	struct pfm_syscall_cookie cookie;
+	void *req, *fptr;
+	unsigned long flags;
+	size_t count;
+	int ret;
+
+	PFM_DBG("fd=%d flags=0x%x type=%d req=%p sz=%zu",
+		fd, uflags, type, ureq, sz);
+
+	if (uflags) {
+		PFM_DBG("no flags defined");
+		return -EINVAL;
+	}
+
+	count = pfm_validate_type_sz(type, sz);
+	if (!count)
+		return -EINVAL;
+
+	ret = pfm_acquire_ctx_from_fd(fd, &ctx, &cookie);
+	if (ret)
+		return ret;
+
+	ret = pfm_get_args(ureq, sz, sizeof(buf), buf, (void **)&req, &fptr);
+	if (ret)
+		goto error;
+
+	spin_lock_irqsave(&ctx->lock, flags);
+
+	ret = pfm_check_task_state(ctx, PFM_CMD_STOPPED, &flags);
+	if (ret)
+		goto skip;
+
+	switch(type) {
+	case PFM_RW_PMD:
+		ret = __pfm_read_pmds(ctx, req, count);
+		break;
+	default:
+		PFM_DBG("invalid type=%d", type);
+		ret = -EINVAL;
+	}
+skip:
+	spin_unlock_irqrestore(&ctx->lock, flags);
+
+	if (copy_to_user(ureq, req, sz))
+		ret = -EFAULT;
+
+	if (fptr)
+		kfree(fptr);
+error:
+	pfm_release_ctx_from_fd(&cookie);
+	return ret;
+}
+
+asmlinkage long sys_pfm_set_state(int fd, int uflags, int state)
+{
+	struct pfm_context *ctx;
+	struct pfm_syscall_cookie cookie;
+	unsigned long flags;
+	int ret;
+
+	PFM_DBG("fd=%d uflags=0x%x state=0x%x", fd, uflags, state);
+
+	if (uflags) {
+		PFM_DBG("no flags defined");
+		return -EINVAL;
+	}
+
+	switch(state) {
+	case PFM_ST_START:
+	case PFM_ST_STOP:
+		break;
+	default:
+		PFM_DBG("invalid state=0x%x", state);
+		return -EINVAL;
+	}
+
+	ret = pfm_acquire_ctx_from_fd(fd, &ctx, &cookie);
+	if (ret)
+		return ret;
+
+	spin_lock_irqsave(&ctx->lock, flags);
+
+	ret = pfm_check_task_state(ctx, PFM_CMD_STOPPED, &flags);
+	if (!ret) {
+		if (state == PFM_ST_STOP)
+			ret = __pfm_stop(ctx);
+		else
+			ret = __pfm_start(ctx);
+	}
+
+	spin_unlock_irqrestore(&ctx->lock, flags);
+
+	pfm_release_ctx_from_fd(&cookie);
+
+	return ret;
+}
+
+static long pfm_detach(int fd, int uflags)
+{
+	struct pfm_context *ctx;
+	struct pfm_syscall_cookie cookie;
+	unsigned long flags;
+	int ret;
+
+	ret = pfm_acquire_ctx_from_fd(fd, &ctx, &cookie);
+	if (ret)
+		return ret;
+
+	spin_lock_irqsave(&ctx->lock, flags);
+
+	ret = pfm_check_task_state(ctx, PFM_CMD_STOPPED|PFM_CMD_UNLOAD, &flags);
+	if (!ret)
+		ret = __pfm_unload_context(ctx);
+
+	spin_unlock_irqrestore(&ctx->lock, flags);
+
+	/*
+	 * if unload was successful, then release the session
+	 * must be called with interrupts enabled, thus we need
+	 * to defer until are out of __pfm_unload_context()
+	 */
+	if (!ret)
+		pfm_session_release();
+
+	pfm_release_ctx_from_fd(&cookie);
+
+	return ret;
+}
+
+asmlinkage long sys_pfm_attach(int fd, int uflags, int target)
+{
+	struct pfm_context *ctx;
+	struct task_struct *task;
+	struct pfm_syscall_cookie cookie;
+	unsigned long flags;
+	int ret;
+
+	PFM_DBG("fd=%d uflags=0x%x target=%d", fd, uflags, target);
+
+	if (uflags) {
+		PFM_DBG("invalid flags");
+		return -EINVAL;
+	}
+
+	/*
+ 	 * handle detach in a separate function
+ 	 */
+	if (target == PFM_NO_TARGET)
+		return pfm_detach(fd, uflags);
+
+	ret = pfm_acquire_ctx_from_fd(fd, &ctx, &cookie);
+	if (ret)
+		return ret;
+
+	task = current;
+
+	/*
+	 * in per-thread mode (not self-monitoring), get a reference
+	 * on task to monitor. This must be done with interrupts enabled
+	 * Upon succesful return, refcount on task has increased.
+	 *
+	 * fget_light() is protecting the context.
+	 */
+   	if (target != current->pid) {
+		ret = pfm_get_task(ctx, target, &task);
+		if (ret)
+			goto error;
+	}
+
+	/*
+	 * irqsave is required to avoid race in case context is already
+	 * loaded or with switch timeout in the case of self-monitoring
+	 */
+	spin_lock_irqsave(&ctx->lock, flags);
+
+	ret = pfm_check_task_state(ctx, PFM_CMD_UNLOADED, &flags);
+	if (!ret)
+		ret = __pfm_load_context(ctx, task);
+
+	spin_unlock_irqrestore(&ctx->lock, flags);
+
+	/*
+	 * in per-thread mode (not self-monitoring), we need
+	 * to decrease refcount on task to monitor:
+	 *   - attach successful: we have a reference in ctx->task
+	 *   - attach failed    : undo the effect of pfm_get_task()
+	 */
+	if (task != current)
+		put_task_struct(task);
+error:
+	pfm_release_ctx_from_fd(&cookie);
+	return ret;
+}
Index: o3/include/linux/perfmon.h
===================================================================
--- o3.orig/include/linux/perfmon.h	2008-10-15 15:53:39.000000000 +0200
+++ o3/include/linux/perfmon.h	2008-10-16 11:49:18.000000000 +0200
@@ -72,6 +72,17 @@
 #define PFM_RW_PMC	0x02 /* accessing PMC registers */
 
 /*
+ * pfm_set_state state:
+ */
+#define PFM_ST_START	0x01 /* start monitoring */
+#define PFM_ST_STOP	0x02 /* stop monitoring */
+
+/*
+ * pfm_attach special target to trigger detach
+ */
+#define PFM_NO_TARGET	-1 /* detach session target */
+
+/*
  * default value for the user and group security parameters in
  * /proc/sys/kernel/perfmon/sys_group
  * /proc/sys/kernel/perfmon/task_group

-- 

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