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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 5/6] xen-gntalloc: Userspace grant allocation driver
On Thu, Feb 03, 2011 at 12:19:03PM -0500, Daniel De Graaf wrote:
> 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: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
> ---
> drivers/xen/Kconfig | 8 +
> drivers/xen/Makefile | 2 +
> drivers/xen/gntalloc.c | 486
> ++++++++++++++++++++++++++++++++++++++++++++++++
> include/xen/gntalloc.h | 50 +++++
> 4 files changed, 546 insertions(+), 0 deletions(-)
> create mode 100644 drivers/xen/gntalloc.c
> create mode 100644 include/xen/gntalloc.h
>
> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
> index 19f1f3c..69d2cd5 100644
> --- a/drivers/xen/Kconfig
> +++ b/drivers/xen/Kconfig
> @@ -142,6 +142,14 @@ 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
> diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
> index 5c3b031..09364b9 100644
> --- a/drivers/xen/Makefile
> +++ b/drivers/xen/Makefile
> @@ -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_XEN_PCIDEV_BACKEND) += pciback/
> obj-$(CONFIG_XENFS) += xenfs/
> obj-$(CONFIG_XEN_SYS_HYPERVISOR) += sys-hypervisor.o
> @@ -19,5 +20,6 @@ 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
> diff --git a/drivers/xen/gntalloc.c b/drivers/xen/gntalloc.c
> new file mode 100644
> index 0000000..d06bf2b
> --- /dev/null
> +++ b/drivers/xen/gntalloc.c
> @@ -0,0 +1,486 @@
> +/******************************************************************************
> + * 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);
So we decrease the gref_size by the count of the ones that we
allocated..
> +
> + list_for_each_entry(gref, &queue_file, next_file) {
> + /* __del_gref does not remove from queue_file */
> + __del_gref(gref);
.. but __del_gref decreases the gref_size by one, so wouldn't
we decrease by too much?
> + }
> +
> + /* 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;
Should we cleanup up priv->index to its earlier value?
> +
> + /* 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@xxxxxxxxxx>, "
> + "Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>");
> +MODULE_DESCRIPTION("User-space grant reference allocator driver");
> diff --git a/include/xen/gntalloc.h b/include/xen/gntalloc.h
> new file mode 100644
> index 0000000..bc3b85e
> --- /dev/null
> +++ b/include/xen/gntalloc.h
> @@ -0,0 +1,50 @@
> +/******************************************************************************
> + * gntalloc.h
> + *
> + * Interface to /dev/xen/gntalloc.
> + *
> + * Author: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
> + *
> + * 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__ */
> --
> 1.7.3.4
>
>
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