3 files changed, 97 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/perf_counter.c b/arch/powerpc/kernel/perf_counter.c
index d05651584d43..e4349281b07d 100644
--- a/arch/powerpc/kernel/perf_counter.c
+++ b/arch/powerpc/kernel/perf_counter.c
@@ -417,6 +417,8 @@ void hw_perf_restore(u64 disable)
                 atomic64_set(&counter->hw.prev_count, val);
                 counter->hw.idx = hwc_index[i] + 1;
                 write_pmc(counter->hw.idx, val);
+                if (counter->user_page)
+                        perf_counter_update_userpage(counter);
         }
         mb();
         cpuhw->mmcr[0] |= MMCR0_PMXE | MMCR0_FCECE;
@@ -572,6 +574,8 @@ static void power_perf_disable(struct perf_counter *counter)
                         ppmu->disable_pmc(counter->hw.idx - 1, cpuhw->mmcr);
                         write_pmc(counter->hw.idx, 0);
                         counter->hw.idx = 0;
+                        if (counter->user_page)
+                                perf_counter_update_userpage(counter);
                         break;
                 }
         }
@@ -698,6 +702,8 @@ static void record_and_restart(struct perf_counter *counter, long val,
         write_pmc(counter->hw.idx, val);
         atomic64_set(&counter->hw.prev_count, val);
         atomic64_set(&counter->hw.period_left, left);
+        if (counter->user_page)
+                perf_counter_update_userpage(counter);
 
         /*
          * Finally record data if requested.
diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 18dc17d0a61c..40b324e91bf6 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -143,6 +143,17 @@ struct perf_counter_hw_event {
 #define PERF_COUNTER_IOC_ENABLE         _IO('$', 0)
 #define PERF_COUNTER_IOC_DISABLE        _IO('$', 1)
 
+/*
+ * Structure of the page that can be mapped via mmap
+ */
+struct perf_counter_mmap_page {
+        __u32   version;                /* version number of this structure */
+        __u32   compat_version;         /* lowest version this is compat with */
+        __u32   lock;                   /* seqlock for synchronization */
+        __u32   index;                  /* hardware counter identifier */
+        __s64   offset;                 /* add to hardware counter value */
+};
+
 #ifdef __KERNEL__
 /*
  * Kernel-internal data types and definitions:
@@ -278,6 +289,9 @@ struct perf_counter {
         int                             oncpu;
         int                             cpu;
 
+        /* pointer to page shared with userspace via mmap */
+        unsigned long                   user_page;
+
         /* read() / irq related data */
         wait_queue_head_t               waitq;
         /* optional: for NMIs */
@@ -361,6 +375,7 @@ extern int perf_counter_task_enable(void);
 extern int hw_perf_group_sched_in(struct perf_counter *group_leader,
                struct perf_cpu_context *cpuctx,
                struct perf_counter_context *ctx, int cpu);
+extern void perf_counter_update_userpage(struct perf_counter *counter);
 
 extern void perf_counter_output(struct perf_counter *counter,
                                 int nmi, struct pt_regs *regs);
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index ce34bff07bda..d9cfd902140e 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -1177,6 +1177,7 @@ static int perf_release(struct inode *inode, struct file *file)
         mutex_unlock(&counter->mutex);
         mutex_unlock(&ctx->mutex);
 
+        free_page(counter->user_page);
         free_counter(counter);
         put_context(ctx);
 
@@ -1346,12 +1347,87 @@ static long perf_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
         return err;
 }
 
+void perf_counter_update_userpage(struct perf_counter *counter)
+{
+        struct perf_counter_mmap_page *userpg;
+
+        if (!counter->user_page)
+                return;
+        userpg = (struct perf_counter_mmap_page *) counter->user_page;
+
+        ++userpg->lock;
+        smp_wmb();
+        userpg->index = counter->hw.idx;
+        userpg->offset = atomic64_read(&counter->count);
+        if (counter->state == PERF_COUNTER_STATE_ACTIVE)
+                userpg->offset -= atomic64_read(&counter->hw.prev_count);
+        smp_wmb();
+        ++userpg->lock;
+}
+
+static int perf_mmap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+        struct perf_counter *counter = vma->vm_file->private_data;
+
+        if (!counter->user_page)
+                return VM_FAULT_SIGBUS;
+
+        vmf->page = virt_to_page(counter->user_page);
+        get_page(vmf->page);
+        return 0;
+}
+
+static struct vm_operations_struct perf_mmap_vmops = {
+        .fault = perf_mmap_fault,
+};
+
+static int perf_mmap(struct file *file, struct vm_area_struct *vma)
+{
+        struct perf_counter *counter = file->private_data;
+        unsigned long userpg;
+
+        if (!(vma->vm_flags & VM_SHARED) || (vma->vm_flags & VM_WRITE))
+                return -EINVAL;
+        if (vma->vm_end - vma->vm_start != PAGE_SIZE)
+                return -EINVAL;
+
+        /*
+         * For now, restrict to the case of a hardware counter
+         * on the current task.
+         */
+        if (is_software_counter(counter) || counter->task != current)
+                return -EINVAL;
+
+        userpg = counter->user_page;
+        if (!userpg) {
+                userpg = get_zeroed_page(GFP_KERNEL);
+                mutex_lock(&counter->mutex);
+                if (counter->user_page) {
+                        free_page(userpg);
+                        userpg = counter->user_page;
+                } else {
+                        counter->user_page = userpg;
+                }
+                mutex_unlock(&counter->mutex);
+                if (!userpg)
+                        return -ENOMEM;
+        }
+
+        perf_counter_update_userpage(counter);
+
+        vma->vm_flags &= ~VM_MAYWRITE;
+        vma->vm_flags |= VM_RESERVED;
+        vma->vm_ops = &perf_mmap_vmops;
+        return 0;
+}
+
 static const struct file_operations perf_fops = {
         .release                = perf_release,
         .read                   = perf_read,
         .poll                   = perf_poll,
         .unlocked_ioctl         = perf_ioctl,
         .compat_ioctl           = perf_ioctl,
+        .mmap                   = perf_mmap,
 };
 
 /*