On 12/14/2010 06:55 AM, 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 | 7 +
> drivers/xen/Makefile | 2 +
> drivers/xen/gntalloc.c | 456
> ++++++++++++++++++++++++++++++++++++++++++++++++
> include/xen/gntalloc.h | 68 +++++++
> 4 files changed, 533 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 fa9982e..8398cb0 100644
> --- a/drivers/xen/Kconfig
> +++ b/drivers/xen/Kconfig
> @@ -180,6 +180,13 @@ config XEN_GNTDEV
> help
> Allows userspace processes 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.
> +
> config XEN_S3
> def_bool y
> depends on XEN_DOM0 && ACPI
> diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
> index ef1ea63..9814c1d 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-$(CONFIG_XEN_BLKDEV_BACKEND) += blkback/
> obj-$(CONFIG_XEN_BLKDEV_TAP) += blktap/
> @@ -25,3 +26,4 @@ obj-$(CONFIG_XEN_PLATFORM_PCI) += platform-pci.o
>
> xen-evtchn-y := evtchn.o
> xen-gntdev-y := gntdev.o
> +xen-gntalloc-y := gntalloc.o
> diff --git a/drivers/xen/gntalloc.c b/drivers/xen/gntalloc.c
> new file mode 100644
> index 0000000..f26adfd
> --- /dev/null
> +++ b/drivers/xen/gntalloc.c
> @@ -0,0 +1,456 @@
> +/******************************************************************************
> + * 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.
> + * 3. X gives the grant reference identifier, GREF, to Y.
> + * 4. A program in Y uses the gntdev device to map the page (owned by X
> + * and identified by GREF) into domain(Y) and then into the address
> + * space of the program. Behind the scenes, this requires a
> + * hypercall in which Xen modifies the host CPU page tables to
> + * perform the sharing -- that's where the actual cross-domain mapping
> + * occurs.
Presumably Y could be any grant-page user, not specifically gntdev? So
you could use this to implement a frontend in userspace?
> + * 5. A program in X mmap()s a segment of the gntalloc device that
> + * corresponds to the shared page.
> + * 6. The two userspace programs can now communicate 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(). You must tear down the sharing in the reverse order
> + * (munmap() and then the destroy 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 <asm/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 <asm/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 debug = 0;
> +module_param(debug, int, 0644);
> +
> +static int limit = 1024;
> +module_param(limit, int, 0644);
> +
> +static LIST_HEAD(gref_list);
> +static DEFINE_SPINLOCK(gref_lock);
> +static int gref_size = 0;
> +
> +/* Metadata on a grant reference. */
> +struct gntalloc_gref {
> + struct list_head next_all; /* list entry gref_list */
> + struct list_head next_file; /* list entry file->list, if open */
> + domid_t foreign_domid; /* The ID of the domain to share with. */
> + grant_ref_t gref_id; /* The grant reference number. */
> + unsigned int users; /* Use count - when zero, waiting on Xen */
> + struct page* page; /* The shared page. */
> +};
> +
> +struct gntalloc_file_private_data {
> + struct list_head list;
> +};
> +
> +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_all) {
> + if (!gref->users)
> + __del_gref(gref);
> + }
> +}
> +
> +
> +static int add_gref(domid_t foreign_domid, uint32_t readonly,
> + struct gntalloc_file_private_data *priv)
> +{
> + int rc;
> + struct gntalloc_gref *gref;
> +
> + rc = -ENOMEM;
> + spin_lock(&gref_lock);
> + do_cleanup();
> + if (gref_size >= limit) {
> + spin_unlock(&gref_lock);
> + rc = -ENOSPC;
> + goto out;
> + }
> + gref_size++;
> + spin_unlock(&gref_lock);
> +
> + gref = kzalloc(sizeof(*gref), GFP_KERNEL);
> + if (!gref)
> + goto out;
> +
> + gref->foreign_domid = foreign_domid;
> + gref->users = 1;
> +
> + /* Allocate the page to share. */
> + gref->page = alloc_page(GFP_KERNEL|__GFP_ZERO);
Could this be GFP_HIGHUSER?
> + if (!gref->page)
> + goto out_nopage;
> +
> + /* Grant foreign access to the page. */
> + gref->gref_id = gnttab_grant_foreign_access(foreign_domid,
> + pfn_to_mfn(page_to_pfn(gref->page)), readonly);
> + if (gref->gref_id < 0) {
> + printk(KERN_ERR "%s: failed to grant foreign access for mfn "
> + "%lu to domain %u\n", __func__,
> + pfn_to_mfn(page_to_pfn(gref->page)), foreign_domid);
> + rc = -EFAULT;
> + goto out_no_foreign_gref;
> + }
> +
> + /* Add to gref lists. */
> + spin_lock(&gref_lock);
> + list_add_tail(&gref->next_all, &gref_list);
> + list_add_tail(&gref->next_file, &priv->list);
> + spin_unlock(&gref_lock);
> +
> + return gref->gref_id;
> +
> +out_no_foreign_gref:
> + __free_page(gref->page);
> +out_nopage:
> + kfree(gref);
> +out:
> + return rc;
> +}
> +
> +static void __del_gref(struct gntalloc_gref *gref)
> +{
> + 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_all);
> +
> + __free_page(gref->page);
> + kfree(gref);
> +}
> +
> +static struct gntalloc_gref* find_gref(struct gntalloc_file_private_data
> *priv,
> + grant_ref_t gref_id)
> +{
> + struct gntalloc_gref *gref;
> + list_for_each_entry(gref, &priv->list, next_file) {
> + if (gref->gref_id == gref_id)
> + return gref;
> + }
> + return NULL;
> +}
> +
> +/*
> + * -------------------------------------
> + * File operations.
> + * -------------------------------------
> + */
> +static int gntalloc_open(struct inode *inode, struct file *filp)
> +{
> + struct gntalloc_file_private_data *priv;
> +
> + try_module_get(THIS_MODULE);
> +
> + priv = kzalloc(sizeof(*priv), GFP_KERNEL);
> + if (!priv)
> + goto out_nomem;
> + INIT_LIST_HEAD(&priv->list);
> +
> + filp->private_data = priv;
> +
> + if (debug)
> + printk("%s: priv %p\n", __FUNCTION__, 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;
> +
> + if (debug)
> + printk("%s: priv %p\n", __FUNCTION__, priv);
> +
> + spin_lock(&gref_lock);
Presumably this is unnecessary because there can be no other users if
you're tearing down the list and destroying priv.
> + 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);
> +
> + module_put(THIS_MODULE);
> +
> + return 0;
> +}
> +
> +static long gntalloc_ioctl_alloc(struct gntalloc_file_private_data *priv,
> + void __user *arg)
> +{
> + int rc = 0;
> + struct ioctl_gntalloc_alloc_gref op;
> +
> + if (debug)
> + printk("%s: priv %p\n", __FUNCTION__, priv);
> +
> + if (copy_from_user(&op, arg, sizeof(op))) {
> + rc = -EFAULT;
> + goto alloc_grant_out;
> + }
> + rc = add_gref(op.foreign_domid, op.readonly, priv);
> + if (rc < 0)
> + goto alloc_grant_out;
> +
> + op.gref_id = rc;
> + op.page_idx = rc;
Hm, see below.
> +
> + rc = 0;
> +
> + if (copy_to_user((void __user *)arg, &op, sizeof(op))) {
> + rc = -EFAULT;
> + goto alloc_grant_out;
> + }
> +
> +alloc_grant_out:
> + return rc;
> +}
> +
> +static long gntalloc_ioctl_dealloc(struct gntalloc_file_private_data *priv,
> + void __user *arg)
> +{
> + int rc = 0;
> + struct ioctl_gntalloc_dealloc_gref op;
> + struct gntalloc_gref *gref;
> +
> + if (debug)
> + printk("%s: priv %p\n", __FUNCTION__, priv);
> +
> + if (copy_from_user(&op, arg, sizeof(op))) {
> + rc = -EFAULT;
> + goto dealloc_grant_out;
> + }
> +
> + spin_lock(&gref_lock);
> + gref = find_gref(priv, op.gref_id);
> + if (gref) {
> + list_del(&gref->next_file);
> + gref->users--;
> + rc = 0;
> + } 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 int gntalloc_vma_fault(struct vm_area_struct *vma, struct vm_fault
> *vmf)
> +{
> + struct gntalloc_gref *gref = vma->vm_private_data;
> + if (!gref)
> + return VM_FAULT_SIGBUS;
> +
> + vmf->page = gref->page;
> + get_page(vmf->page);
> +
> + 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 = {
> + .fault = gntalloc_vma_fault,
> + .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;
> +
> + if (debug)
> + printk("%s: priv %p, page %lu\n", __func__,
> + priv, vma->vm_pgoff);
> +
> + /*
> + * There is a 1-to-1 correspondence of grant references to shared
> + * pages, so it only makes sense to map exactly one page per
> + * call to mmap().
> + */
Single-page mmap makes sense if the only possible use-cases are for
single-page mappings, but if you're talking about framebuffers and the
like is seems like a very awkward way to use mmap. It would be cleaner
from an API perspective to have a user-mode defined flat address space
indexed by pgoff which maps to an array of grefs, so you can sensibly do
a multi-page mapping.
It would also allow you to hide the grefs from usermode entirely. Then
its just up to usermode to choose suitable file offsets for itself.
> + if (((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) != 1) {
> + printk(KERN_ERR "%s: Only one page can be memory-mapped "
> + "per grant reference.\n", __func__);
> + return -EINVAL;
> + }
> +
> + if (!(vma->vm_flags & VM_SHARED)) {
> + printk(KERN_ERR "%s: Mapping must be shared.\n",
> + __func__);
> + return -EINVAL;
> + }
> +
> + spin_lock(&gref_lock);
> + gref = find_gref(priv, vma->vm_pgoff);
> + if (gref == NULL) {
> + spin_unlock(&gref_lock);
> + printk(KERN_ERR "%s: Could not find a grant reference with "
> + "page index %lu.\n", __func__, vma->vm_pgoff);
> + return -ENOENT;
> + }
> + gref->users++;
> + spin_unlock(&gref_lock);
> +
> + vma->vm_private_data = gref;
> +
> + /* This flag prevents Bad PTE errors when the memory is unmapped. */
> + vma->vm_flags |= VM_RESERVED;
> + vma->vm_flags |= VM_DONTCOPY;
> + vma->vm_flags |= VM_IO;
If you set VM_PFNMAP then you don't need to deal with faults.
> +
> + vma->vm_ops = &gntalloc_vmops;
> +
> + return 0;
> +}
> +
> +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()) {
> + if (debug)
> + printk(KERN_ERR "gntalloc: You must be running Xen\n");
> + return -ENODEV;
> + }
> +
> + err = misc_register(&gntalloc_miscdev);
> + if (err != 0) {
> + printk(KERN_ERR "Could not register misc gntalloc device\n");
> + return err;
> + }
> +
> + if (debug)
> + printk(KERN_INFO "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..76b70d7
> --- /dev/null
> +++ b/include/xen/gntalloc.h
> @@ -0,0 +1,68 @@
> +/******************************************************************************
> + * gntalloc.h
> + *
> + * Interface to /dev/xen/gntalloc.
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License version 2
> + * as published by the Free Software Foundation; or, when distributed
> + * separately from the Linux kernel or incorporated into other
> + * software packages, subject to the following license:
> + *
> + * Permission is hereby granted, free of charge, to any person obtaining a
> copy
> + * of this source file (the "Software"), to deal in the Software without
> + * restriction, including without limitation the rights to use, copy, modify,
> + * merge, publish, distribute, sublicense, and/or sell copies of the
> Software,
> + * and to permit persons to whom the Software is furnished to do so, subject
> to
> + * the following conditions:
> + *
> + * The above copyright notice and this permission notice shall be included in
> + * all copies or substantial portions of the Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
> THE
> + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
> + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
> DEALINGS
> + * IN THE SOFTWARE.
> + */
> +
> +#ifndef __LINUX_PUBLIC_GNTALLOC_H__
> +#define __LINUX_PUBLIC_GNTALLOC_H__
> +
> +/*
> + * Allocates a new page and creates a new grant reference.
> + *
> + * N.B. The page_idx is really the address >> PAGE_SHIFT, meaning it's the
> + * page number and not an actual address. It must be shifted again prior
> + * to feeding it to mmap() (i.e. page_idx << PAGE_SHIFT).
> + */
> +#define IOCTL_GNTALLOC_ALLOC_GREF \
> +_IOC(_IOC_NONE, 'G', 1, sizeof(struct ioctl_gntalloc_alloc_gref))
> +struct ioctl_gntalloc_alloc_gref {
> + /* IN parameters */
> + /* The ID of the domain creating the grant reference. */
> + domid_t owner_domid;
> + /* The ID of the domain to be given access to the grant. */
> + domid_t foreign_domid;
> + /* The type of access given to domid. */
> + uint32_t readonly;
> + /* OUT parameters */
> + /* The grant reference of the newly created grant. */
> + grant_ref_t gref_id;
> + /* The page index (page number, NOT address) for grant mmap(). */
> + uint32_t page_idx;
> +};
> +
> +/*
> + * Deallocates the grant reference, freeing the associated page.
> + */
> +#define IOCTL_GNTALLOC_DEALLOC_GREF \
> +_IOC(_IOC_NONE, 'G', 2, sizeof(struct ioctl_gntalloc_dealloc_gref))
> +struct ioctl_gntalloc_dealloc_gref {
> + /* IN parameter */
> + /* The grant reference to deallocate. */
> + grant_ref_t gref_id;
> +};
> +#endif /* __LINUX_PUBLIC_GNTALLOC_H__ */
J
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