Commit dd314058 authored by Daniel De Graaf's avatar Daniel De Graaf Committed by Konrad Rzeszutek Wilk

xen-gntalloc: Userspace grant allocation driver

This allows a userspace application to allocate a shared page for
implementing inter-domain communication or device drivers. These
shared pages can be mapped using the gntdev device or by the kernel
in another domain.
Signed-off-by: default avatarDaniel De Graaf <dgdegra@tycho.nsa.gov>
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent aab8f11a
......@@ -80,6 +80,14 @@ config XEN_GNTDEV
help
Allows userspace processes to use grants.
config XEN_GRANT_DEV_ALLOC
tristate "User-space grant reference allocator driver"
depends on XEN
help
Allows userspace processes to create pages with access granted
to other domains. This can be used to implement frontend drivers
or as part of an inter-domain shared memory channel.
config XEN_PLATFORM_PCI
tristate "xen platform pci device driver"
depends on XEN_PVHVM && PCI
......
......@@ -10,6 +10,7 @@ obj-$(CONFIG_XEN_XENCOMM) += xencomm.o
obj-$(CONFIG_XEN_BALLOON) += balloon.o
obj-$(CONFIG_XEN_DEV_EVTCHN) += xen-evtchn.o
obj-$(CONFIG_XEN_GNTDEV) += xen-gntdev.o
obj-$(CONFIG_XEN_GRANT_DEV_ALLOC) += xen-gntalloc.o
obj-$(CONFIG_XENFS) += xenfs/
obj-$(CONFIG_XEN_SYS_HYPERVISOR) += sys-hypervisor.o
obj-$(CONFIG_XEN_PLATFORM_PCI) += xen-platform-pci.o
......@@ -18,5 +19,6 @@ obj-$(CONFIG_XEN_DOM0) += pci.o
xen-evtchn-y := evtchn.o
xen-gntdev-y := gntdev.o
xen-gntalloc-y := gntalloc.o
xen-platform-pci-y := platform-pci.o
/******************************************************************************
* gntalloc.c
*
* Device for creating grant references (in user-space) that may be shared
* with other domains.
*
* 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
*/
/*
* This driver exists to allow userspace programs in Linux to allocate kernel
* memory that will later be shared with another domain. Without this device,
* Linux userspace programs cannot create grant references.
*
* How this stuff works:
* X -> granting a page to Y
* Y -> mapping the grant from X
*
* 1. X uses the gntalloc device to allocate a page of kernel memory, P.
* 2. X creates an entry in the grant table that says domid(Y) can access P.
* This is done without a hypercall unless the grant table needs expansion.
* 3. X gives the grant reference identifier, GREF, to Y.
* 4. Y maps the page, either directly into kernel memory for use in a backend
* driver, or via a the gntdev device to map into the address space of an
* application running in Y. This is the first point at which Xen does any
* tracking of the page.
* 5. A program in X mmap()s a segment of the gntalloc device that corresponds
* to the shared page, and can now communicate with Y over the shared page.
*
*
* NOTE TO USERSPACE LIBRARIES:
* The grant allocation and mmap()ing are, naturally, two separate operations.
* You set up the sharing by calling the create ioctl() and then the mmap().
* Teardown requires munmap() and either close() or ioctl().
*
* WARNING: Since Xen does not allow a guest to forcibly end the use of a grant
* reference, this device can be used to consume kernel memory by leaving grant
* references mapped by another domain when an application exits. Therefore,
* there is a global limit on the number of pages that can be allocated. When
* all references to the page are unmapped, it will be freed during the next
* grant operation.
*/
#include <linux/atomic.h>
#include <linux/module.h>
#include <linux/miscdevice.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/device.h>
#include <linux/mm.h>
#include <linux/uaccess.h>
#include <linux/types.h>
#include <linux/list.h>
#include <xen/xen.h>
#include <xen/page.h>
#include <xen/grant_table.h>
#include <xen/gntalloc.h>
static int limit = 1024;
module_param(limit, int, 0644);
MODULE_PARM_DESC(limit, "Maximum number of grants that may be allocated by "
"the gntalloc device");
static LIST_HEAD(gref_list);
static DEFINE_SPINLOCK(gref_lock);
static int gref_size;
/* Metadata on a grant reference. */
struct gntalloc_gref {
struct list_head next_gref; /* list entry gref_list */
struct list_head next_file; /* list entry file->list, if open */
struct page *page; /* The shared page */
uint64_t file_index; /* File offset for mmap() */
unsigned int users; /* Use count - when zero, waiting on Xen */
grant_ref_t gref_id; /* The grant reference number */
};
struct gntalloc_file_private_data {
struct list_head list;
uint64_t index;
};
static void __del_gref(struct gntalloc_gref *gref);
static void do_cleanup(void)
{
struct gntalloc_gref *gref, *n;
list_for_each_entry_safe(gref, n, &gref_list, next_gref) {
if (!gref->users)
__del_gref(gref);
}
}
static int add_grefs(struct ioctl_gntalloc_alloc_gref *op,
uint32_t *gref_ids, struct gntalloc_file_private_data *priv)
{
int i, rc, readonly;
LIST_HEAD(queue_gref);
LIST_HEAD(queue_file);
struct gntalloc_gref *gref;
readonly = !(op->flags & GNTALLOC_FLAG_WRITABLE);
rc = -ENOMEM;
for (i = 0; i < op->count; i++) {
gref = kzalloc(sizeof(*gref), GFP_KERNEL);
if (!gref)
goto undo;
list_add_tail(&gref->next_gref, &queue_gref);
list_add_tail(&gref->next_file, &queue_file);
gref->users = 1;
gref->file_index = op->index + i * PAGE_SIZE;
gref->page = alloc_page(GFP_KERNEL|__GFP_ZERO);
if (!gref->page)
goto undo;
/* Grant foreign access to the page. */
gref->gref_id = gnttab_grant_foreign_access(op->domid,
pfn_to_mfn(page_to_pfn(gref->page)), readonly);
if (gref->gref_id < 0) {
rc = gref->gref_id;
goto undo;
}
gref_ids[i] = gref->gref_id;
}
/* Add to gref lists. */
spin_lock(&gref_lock);
list_splice_tail(&queue_gref, &gref_list);
list_splice_tail(&queue_file, &priv->list);
spin_unlock(&gref_lock);
return 0;
undo:
spin_lock(&gref_lock);
gref_size -= (op->count - i);
list_for_each_entry(gref, &queue_file, next_file) {
/* __del_gref does not remove from queue_file */
__del_gref(gref);
}
/* It's possible for the target domain to map the just-allocated grant
* references by blindly guessing their IDs; if this is done, then
* __del_gref will leave them in the queue_gref list. They need to be
* added to the global list so that we can free them when they are no
* longer referenced.
*/
if (unlikely(!list_empty(&queue_gref)))
list_splice_tail(&queue_gref, &gref_list);
spin_unlock(&gref_lock);
return rc;
}
static void __del_gref(struct gntalloc_gref *gref)
{
if (gref->gref_id > 0) {
if (gnttab_query_foreign_access(gref->gref_id))
return;
if (!gnttab_end_foreign_access_ref(gref->gref_id, 0))
return;
}
gref_size--;
list_del(&gref->next_gref);
if (gref->page)
__free_page(gref->page);
kfree(gref);
}
/* finds contiguous grant references in a file, returns the first */
static struct gntalloc_gref *find_grefs(struct gntalloc_file_private_data *priv,
uint64_t index, uint32_t count)
{
struct gntalloc_gref *rv = NULL, *gref;
list_for_each_entry(gref, &priv->list, next_file) {
if (gref->file_index == index && !rv)
rv = gref;
if (rv) {
if (gref->file_index != index)
return NULL;
index += PAGE_SIZE;
count--;
if (count == 0)
return rv;
}
}
return NULL;
}
/*
* -------------------------------------
* File operations.
* -------------------------------------
*/
static int gntalloc_open(struct inode *inode, struct file *filp)
{
struct gntalloc_file_private_data *priv;
priv = kzalloc(sizeof(*priv), GFP_KERNEL);
if (!priv)
goto out_nomem;
INIT_LIST_HEAD(&priv->list);
filp->private_data = priv;
pr_debug("%s: priv %p\n", __func__, priv);
return 0;
out_nomem:
return -ENOMEM;
}
static int gntalloc_release(struct inode *inode, struct file *filp)
{
struct gntalloc_file_private_data *priv = filp->private_data;
struct gntalloc_gref *gref;
pr_debug("%s: priv %p\n", __func__, priv);
spin_lock(&gref_lock);
while (!list_empty(&priv->list)) {
gref = list_entry(priv->list.next,
struct gntalloc_gref, next_file);
list_del(&gref->next_file);
gref->users--;
if (gref->users == 0)
__del_gref(gref);
}
kfree(priv);
spin_unlock(&gref_lock);
return 0;
}
static long gntalloc_ioctl_alloc(struct gntalloc_file_private_data *priv,
struct ioctl_gntalloc_alloc_gref __user *arg)
{
int rc = 0;
struct ioctl_gntalloc_alloc_gref op;
uint32_t *gref_ids;
pr_debug("%s: priv %p\n", __func__, priv);
if (copy_from_user(&op, arg, sizeof(op))) {
rc = -EFAULT;
goto out;
}
gref_ids = kzalloc(sizeof(gref_ids[0]) * op.count, GFP_TEMPORARY);
if (!gref_ids) {
rc = -ENOMEM;
goto out;
}
spin_lock(&gref_lock);
/* Clean up pages that were at zero (local) users but were still mapped
* by remote domains. Since those pages count towards the limit that we
* are about to enforce, removing them here is a good idea.
*/
do_cleanup();
if (gref_size + op.count > limit) {
spin_unlock(&gref_lock);
rc = -ENOSPC;
goto out_free;
}
gref_size += op.count;
op.index = priv->index;
priv->index += op.count * PAGE_SIZE;
spin_unlock(&gref_lock);
rc = add_grefs(&op, gref_ids, priv);
if (rc < 0)
goto out_free;
/* Once we finish add_grefs, it is unsafe to touch the new reference,
* since it is possible for a concurrent ioctl to remove it (by guessing
* its index). If the userspace application doesn't provide valid memory
* to write the IDs to, then it will need to close the file in order to
* release - which it will do by segfaulting when it tries to access the
* IDs to close them.
*/
if (copy_to_user(arg, &op, sizeof(op))) {
rc = -EFAULT;
goto out_free;
}
if (copy_to_user(arg->gref_ids, gref_ids,
sizeof(gref_ids[0]) * op.count)) {
rc = -EFAULT;
goto out_free;
}
out_free:
kfree(gref_ids);
out:
return rc;
}
static long gntalloc_ioctl_dealloc(struct gntalloc_file_private_data *priv,
void __user *arg)
{
int i, rc = 0;
struct ioctl_gntalloc_dealloc_gref op;
struct gntalloc_gref *gref, *n;
pr_debug("%s: priv %p\n", __func__, priv);
if (copy_from_user(&op, arg, sizeof(op))) {
rc = -EFAULT;
goto dealloc_grant_out;
}
spin_lock(&gref_lock);
gref = find_grefs(priv, op.index, op.count);
if (gref) {
/* Remove from the file list only, and decrease reference count.
* The later call to do_cleanup() will remove from gref_list and
* free the memory if the pages aren't mapped anywhere.
*/
for (i = 0; i < op.count; i++) {
n = list_entry(gref->next_file.next,
struct gntalloc_gref, next_file);
list_del(&gref->next_file);
gref->users--;
gref = n;
}
} else {
rc = -EINVAL;
}
do_cleanup();
spin_unlock(&gref_lock);
dealloc_grant_out:
return rc;
}
static long gntalloc_ioctl(struct file *filp, unsigned int cmd,
unsigned long arg)
{
struct gntalloc_file_private_data *priv = filp->private_data;
switch (cmd) {
case IOCTL_GNTALLOC_ALLOC_GREF:
return gntalloc_ioctl_alloc(priv, (void __user *)arg);
case IOCTL_GNTALLOC_DEALLOC_GREF:
return gntalloc_ioctl_dealloc(priv, (void __user *)arg);
default:
return -ENOIOCTLCMD;
}
return 0;
}
static void gntalloc_vma_close(struct vm_area_struct *vma)
{
struct gntalloc_gref *gref = vma->vm_private_data;
if (!gref)
return;
spin_lock(&gref_lock);
gref->users--;
if (gref->users == 0)
__del_gref(gref);
spin_unlock(&gref_lock);
}
static struct vm_operations_struct gntalloc_vmops = {
.close = gntalloc_vma_close,
};
static int gntalloc_mmap(struct file *filp, struct vm_area_struct *vma)
{
struct gntalloc_file_private_data *priv = filp->private_data;
struct gntalloc_gref *gref;
int count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
int rv, i;
pr_debug("%s: priv %p, page %lu+%d\n", __func__,
priv, vma->vm_pgoff, count);
if (!(vma->vm_flags & VM_SHARED)) {
printk(KERN_ERR "%s: Mapping must be shared.\n", __func__);
return -EINVAL;
}
spin_lock(&gref_lock);
gref = find_grefs(priv, vma->vm_pgoff << PAGE_SHIFT, count);
if (gref == NULL) {
rv = -ENOENT;
pr_debug("%s: Could not find grant reference",
__func__);
goto out_unlock;
}
vma->vm_private_data = gref;
vma->vm_flags |= VM_RESERVED;
vma->vm_flags |= VM_DONTCOPY;
vma->vm_flags |= VM_PFNMAP | VM_PFN_AT_MMAP;
vma->vm_ops = &gntalloc_vmops;
for (i = 0; i < count; i++) {
gref->users++;
rv = vm_insert_page(vma, vma->vm_start + i * PAGE_SIZE,
gref->page);
if (rv)
goto out_unlock;
gref = list_entry(gref->next_file.next,
struct gntalloc_gref, next_file);
}
rv = 0;
out_unlock:
spin_unlock(&gref_lock);
return rv;
}
static const struct file_operations gntalloc_fops = {
.owner = THIS_MODULE,
.open = gntalloc_open,
.release = gntalloc_release,
.unlocked_ioctl = gntalloc_ioctl,
.mmap = gntalloc_mmap
};
/*
* -------------------------------------
* Module creation/destruction.
* -------------------------------------
*/
static struct miscdevice gntalloc_miscdev = {
.minor = MISC_DYNAMIC_MINOR,
.name = "xen/gntalloc",
.fops = &gntalloc_fops,
};
static int __init gntalloc_init(void)
{
int err;
if (!xen_domain())
return -ENODEV;
err = misc_register(&gntalloc_miscdev);
if (err != 0) {
printk(KERN_ERR "Could not register misc gntalloc device\n");
return err;
}
pr_debug("Created grant allocation device at %d,%d\n",
MISC_MAJOR, gntalloc_miscdev.minor);
return 0;
}
static void __exit gntalloc_exit(void)
{
misc_deregister(&gntalloc_miscdev);
}
module_init(gntalloc_init);
module_exit(gntalloc_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Carter Weatherly <carter.weatherly@jhuapl.edu>, "
"Daniel De Graaf <dgdegra@tycho.nsa.gov>");
MODULE_DESCRIPTION("User-space grant reference allocator driver");
/******************************************************************************
* gntalloc.h
*
* Interface to /dev/xen/gntalloc.
*
* Author: Daniel De Graaf <dgdegra@tycho.nsa.gov>
*
* This file is in the public domain.
*/
#ifndef __LINUX_PUBLIC_GNTALLOC_H__
#define __LINUX_PUBLIC_GNTALLOC_H__
/*
* Allocates a new page and creates a new grant reference.
*/
#define IOCTL_GNTALLOC_ALLOC_GREF \
_IOC(_IOC_NONE, 'G', 5, sizeof(struct ioctl_gntalloc_alloc_gref))
struct ioctl_gntalloc_alloc_gref {
/* IN parameters */
/* The ID of the domain to be given access to the grants. */
uint16_t domid;
/* Flags for this mapping */
uint16_t flags;
/* Number of pages to map */
uint32_t count;
/* OUT parameters */
/* The offset to be used on a subsequent call to mmap(). */
uint64_t index;
/* The grant references of the newly created grant, one per page */
/* Variable size, depending on count */
uint32_t gref_ids[1];
};
#define GNTALLOC_FLAG_WRITABLE 1
/*
* Deallocates the grant reference, allowing the associated page to be freed if
* no other domains are using it.
*/
#define IOCTL_GNTALLOC_DEALLOC_GREF \
_IOC(_IOC_NONE, 'G', 6, sizeof(struct ioctl_gntalloc_dealloc_gref))
struct ioctl_gntalloc_dealloc_gref {
/* IN parameters */
/* The offset returned in the map operation */
uint64_t index;
/* Number of references to unmap */
uint32_t count;
};
#endif /* __LINUX_PUBLIC_GNTALLOC_H__ */
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