Really simple example of using get_user_pages and memory aligned allocation using posix_memalign. Hope this helps!

awesome.patch

diff -PurN dummy/gu_page.c get_user_pages/gu_page.c
--- dummy/gu_page.c	1970-01-01 01:00:00.000000000 +0100
+++ get_user_pages/gu_page.c	2012-06-14 14:41:31.797310260 +0100
@@ -0,0 +1,124 @@
+#include <linux/module.h>
+#include <linux/mm.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+
+#include <linux/init.h>
+#include <linux/device.h>
+#include <linux/fs.h>
+#include <asm/uaccess.h>
+#include <asm/errno.h>
+
+#include <linux/pagemap.h>
+
+#define LED_MAJOR 42
+#define DEVICE_NAME "simpleuser"
+
+/*
+ * Prototypes
+ */
+static int device_open(struct inode *, struct file *);
+static int device_release(struct inode *, struct file *);
+static ssize_t device_write(struct file *filp, const char __user *buf, size_t count, loff_t * ppos);
+
+static struct file_operations led_ops = {
+	.owner    = THIS_MODULE,
+	.open     = device_open,
+	.release  = device_release,
+	.write =	device_write
+};
+
+static struct class *mmap_class;
+
+static int device_open(struct inode *inode, struct file *file)
+{
+	printk ("device_open: %d.%d\n", MAJOR (inode->i_rdev),
+		 MINOR (inode->i_rdev));
+	return 0;
+}
+
+static int device_release(struct inode *inode, struct file *file)
+{
+	pr_info("device_release: %d.%d\n", MAJOR (inode->i_rdev),
+		 MINOR (inode->i_rdev));
+	return 0;
+}
+
+static ssize_t device_write(struct file *filp, const char __user *buf, size_t count, loff_t * ppos)
+{
+    int res;
+    unsigned long uaddr;
+    char addrstr[80];
+    struct page *page;
+    char *my_page_address;
+
+    unsigned long copied = copy_from_user(addrstr, buf, sizeof(addrstr));
+    if (copied != 0)
+    {
+        pr_err("Told to copy %d, but only copied %lu\n", count, copied);
+    }
+    uaddr = simple_strtoul(addrstr, NULL, 0);
+    
+    down_read(&current->mm->mmap_sem);
+	res = get_user_pages(current, current->mm,
+		                 uaddr,
+		                 1, /* Only want one page */
+		                 1, /* Do want to write into it */
+		                 1, /* do force */
+		                 &page,
+		                 NULL);
+    if (res == 1) {
+        pr_err("Got page\n");
+        /* Do something with it */
+        my_page_address = kmap(page);
+        strcpy (my_page_address, "Hello, is it me you're looking for?\n");
+        pr_err("Got address %p and user told me it was %lx\n",my_page_address, uaddr);
+        pr_err("Wrote: %s", my_page_address);
+        
+        kunmap(page);
+        
+        /* Clean up */
+    if (!PageReserved(page))
+        SetPageDirty(page);
+	    page_cache_release(page);
+    } else {
+        pr_err("Couldn't get page :(\n");
+    }
+	up_read(&current->mm->mmap_sem);
+    
+    
+    return count;
+}
+
+static int __init el504_init(void)
+{
+	int ret ;
+	
+	/* Register the character device */
+	ret = register_chrdev (LED_MAJOR, DEVICE_NAME, &led_ops);
+	if (ret < 0) {
+		pr_alert("el504_init: failed with %d\n", ret);
+		return ret;
+	}
+
+	mmap_class = class_create (THIS_MODULE, "mmap");
+	device_create (mmap_class, NULL, MKDEV (LED_MAJOR, 0), NULL, "mmap");
+	return 0;
+}
+
+static void __exit el504_exit(void)
+{
+	pr_debug("Goodbye\n");
+	device_destroy (mmap_class, MKDEV (LED_MAJOR, 0));
+	class_destroy (mmap_class);
+	unregister_chrdev (LED_MAJOR, DEVICE_NAME);
+}
+
+module_init (el504_init);
+module_exit (el504_exit);
+
+MODULE_LICENSE ("GPL");
+MODULE_AUTHOR ("Nick Glynn");
+MODULE_DESCRIPTION ("Example for get_user_pages()");
+
diff -PurN dummy/Makefile get_user_pages/Makefile
--- dummy/Makefile	1970-01-01 01:00:00.000000000 +0100
+++ get_user_pages/Makefile	2012-06-14 14:21:11.271274011 +0100
@@ -0,0 +1,9 @@
+obj-m += gu_page.o
+KDIR := /lib/modules/$(shell uname -r)/build
+PWD := $(shell pwd)
+
+all:
+	$(MAKE) -C $(KDIR) M=$(PWD) modules
+clean:
+	$(MAKE) -C $(KDIR) M=$(PWD) clean 
+
diff -PurN dummy/userspace/Makefile get_user_pages/userspace/Makefile
--- dummy/userspace/Makefile	1970-01-01 01:00:00.000000000 +0100
+++ get_user_pages/userspace/Makefile	2012-06-14 14:53:29.528816418 +0100
@@ -0,0 +1,8 @@
+BIN := userspace
+OBJECTS += $(BIN).c
+
+all:
+	gcc $(OBJECTS) -o $(BIN)
+
+clean:
+	rm $(BIN)
diff -PurN dummy/userspace/userspace.c get_user_pages/userspace/userspace.c
--- dummy/userspace/userspace.c	1970-01-01 01:00:00.000000000 +0100
+++ get_user_pages/userspace/userspace.c	2012-06-14 14:47:25.754137234 +0100
@@ -0,0 +1,51 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <string.h>
+
+int main (int argc, char *argv[])
+{
+	int mh, res;
+       char addrstr[80];
+	char *ptr, *bp;
+	const char *string = "Testing page";
+
+	printf ("%s\n", argv[0]);
+	if (argc < 2)
+	{
+		printf ("Usage: %s <file>\n", argv[0]);
+		return 1;
+	}
+	mh = open (argv [1], O_RDWR);
+	if (mh == -1)
+	{
+		printf ("Unable to open '%s'\n", argv [1]);
+		return 1;
+	}
+	/* Grab a page of memory (4096) and sprintf into it */
+	
+	res = posix_memalign((void **)&ptr, 4096, 4096);
+
+	if (NULL != ptr)
+	{
+	    sprintf(ptr, "%s", string);
+	
+	    bp = ptr;
+	
+	    /* Do a write to the kernel at which point it should mess with it */
+	    sprintf(addrstr, "%p", ptr);
+	    printf("Telling kernel it is %p\n", ptr);
+           res = write(mh, addrstr, strlen(addrstr));
+	
+	    /* See what lives there still */
+	    printf ("Marker text 1: %s\n", ptr);
+	    printf ("ptr = %p, bp = %p\n", ptr, bp);
+
+    }
+    close (mh);
+	return 0;
+}

The point of this code was to setup some page-aligned memory in user space, pass the address to the kernel and then have the kernel mess with it to highlight how you can use get_user_pages.

There's a lot of debuggy stuff in there and it's clearly sample code but I struggled to find decent examples on how to do what I wanted to do (allocate my own memory) so hopefully this should help some people out.

@17twnty

...
unsigned long copied = copy_from_user(addrstr, buf, sizeof(addrstr));
if (copied != 0)
{
    pr_err("Told to copy %d, but only copied %lu\n", count, copied);
}
...

You'll need to check copy_from_user result for -EFAULT at least.

@17twenty. Thanks!....You are indeed helping out other!

And 8 years later somebody still wants to look at this! Thankyou so much for sharing this. I am grateful for it.

@17twenty Thank you! I traced from LWM Zero Copy.
Latest drivers/scsi/st.c also helful :)