[Xen-devel] [PATCH 2/3] xen-fbfront: Use grant references when requested

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

The current version of the Xen framebuffer API passes MFNs directly
to the backend driver, which requires the backend to have full access
to this domain's memory. Add a parameter in xenbus to request the use of
grant entries instead, which are slightly slower to map but provide
inter-domain isolation.

Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
---
 drivers/video/xen-fbfront.c |   73 +++++++++++++++++++++++++++++++++---------
 1 files changed, 57 insertions(+), 16 deletions(-)

diff --git a/drivers/video/xen-fbfront.c b/drivers/video/xen-fbfront.c
index 56d6061..b3107e4 100644
--- a/drivers/video/xen-fbfront.c
+++ b/drivers/video/xen-fbfront.c
@@ -11,13 +11,6 @@
  *  more details.
  */
 
-/*
- * TODO:
- *
- * Switch to grant tables when they become capable of dealing with the
- * frame buffer.
- */
-
 #include <linux/console.h>
 #include <linux/kernel.h>
 #include <linux/errno.h>
@@ -32,6 +25,8 @@
 #include <xen/xen.h>
 #include <xen/events.h>
 #include <xen/page.h>
+#include <xen/grant_table.h>
+#include <xen/interface/grant_table.h>
 #include <xen/interface/io/fbif.h>
 #include <xen/interface/io/protocols.h>
 #include <xen/xenbus.h>
@@ -46,6 +41,7 @@ struct xenfb_info {
        int                     irq;
        struct xenfb_page       *page;
        unsigned long           *mfns;
+       int                     page_gref;
        int                     update_wanted; /* XENFB_TYPE_UPDATE wanted */
        int                     feature_resize; /* XENFB_TYPE_RESIZE ok */
        struct xenfb_resize     resize;         /* protected by resize_lock */
@@ -65,7 +61,7 @@ MODULE_PARM_DESC(video,
 
 static void xenfb_make_preferred_console(void);
 static int xenfb_remove(struct xenbus_device *);
-static void xenfb_init_shared_page(struct xenfb_info *, struct fb_info *);
+static void xenfb_init_shared_page(struct xenbus_device *, struct xenfb_info 
*, struct fb_info *);
 static int xenfb_connect_backend(struct xenbus_device *, struct xenfb_info *);
 static void xenfb_disconnect_backend(struct xenfb_info *);
 
@@ -474,7 +470,7 @@ static int __devinit xenfb_probe(struct xenbus_device *dev,
        fb_info->fbdefio = &xenfb_defio;
        fb_deferred_io_init(fb_info);
 
-       xenfb_init_shared_page(info, fb_info);
+       xenfb_init_shared_page(dev, info, fb_info);
 
        ret = xenfb_connect_backend(dev, info);
        if (ret < 0)
@@ -528,7 +524,7 @@ static int xenfb_resume(struct xenbus_device *dev)
        struct xenfb_info *info = dev_get_drvdata(&dev->dev);
 
        xenfb_disconnect_backend(info);
-       xenfb_init_shared_page(info, info->fb_info);
+       xenfb_init_shared_page(dev, info, info->fb_info);
        return xenfb_connect_backend(dev, info);
 }
 
@@ -556,17 +552,58 @@ static unsigned long vmalloc_to_mfn(void *address)
        return pfn_to_mfn(vmalloc_to_pfn(address));
 }
 
-static void xenfb_init_shared_page(struct xenfb_info *info,
+static void xenfb_init_shared_page(struct xenbus_device *dev,
+                                   struct xenfb_info *info,
                                   struct fb_info *fb_info)
 {
-       int i;
        int epd = PAGE_SIZE / sizeof(info->mfns[0]);
+       int be_id = dev->otherend_id;
+       int i, ref;
+       unsigned long mfn;
+       grant_ref_t gref_head;
+       int allpages = info->nr_pages + ((info->nr_pages + epd - 1) / epd) + 1;
+
+       int grants = 0;
+       xenbus_scanf(XBT_NIL, dev->otherend, "feature-grants", "%d", &grants);
+
+       if (grants) {
+               int err = gnttab_alloc_grant_references(allpages, &gref_head);
+               if (err < 0) {
+                       xenbus_dev_fatal(dev, err, "fbdev grant refs");
+                       info->page_gref = -ENOSPC;
+               } else {
+                       ref = gnttab_claim_grant_reference(&gref_head);
+                       mfn = virt_to_mfn(info->page);
+                       BUG_ON(ref == -ENOSPC);
+                       gnttab_grant_foreign_access_ref(ref, be_id, mfn, 0);
+                       info->page_gref = ref;
+               }
+       } else
+               info->page_gref = -ENOENT;
 
        for (i = 0; i < info->nr_pages; i++)
-               info->mfns[i] = vmalloc_to_mfn(info->fb + i * PAGE_SIZE);
+       {
+               mfn = vmalloc_to_mfn(info->fb + i * PAGE_SIZE);
+               if (grants) {
+                       ref = gnttab_claim_grant_reference(&gref_head);
+                       BUG_ON(ref == -ENOSPC);
+                       gnttab_grant_foreign_access_ref(ref, be_id, mfn, 1);
+                       info->mfns[i] = ref;
+               } else
+                       info->mfns[i] = mfn;
+       }
 
        for (i = 0; i * epd < info->nr_pages; i++)
-               info->page->pd[i] = vmalloc_to_mfn(&info->mfns[i * epd]);
+       {
+               mfn = vmalloc_to_mfn(&info->mfns[i * epd]);
+               if (grants) {
+                       ref = gnttab_claim_grant_reference(&gref_head);
+                       BUG_ON(ref == -ENOSPC);
+                       gnttab_grant_foreign_access_ref(ref, be_id, mfn, 1);
+                       info->page->pd[i] = ref;
+               } else
+                       info->page->pd[i] = mfn;
+       }
 
        info->page->width = fb_info->var.xres;
        info->page->height = fb_info->var.yres;
@@ -599,8 +636,12 @@ static int xenfb_connect_backend(struct xenbus_device *dev,
                xenbus_dev_fatal(dev, ret, "starting transaction");
                goto unbind_irq;
        }
-       ret = xenbus_printf(xbt, dev->nodename, "page-ref", "%lu",
-                           virt_to_mfn(info->page));
+       if (info->page_gref < 0)
+               ret = xenbus_printf(xbt, dev->nodename, "page-ref", "%lu",
+                                   virt_to_mfn(info->page));
+       else
+               ret = xenbus_printf(xbt, dev->nodename, "page-gref", "%u",
+                                   info->page_gref);
        if (ret)
                goto error_xenbus;
        ret = xenbus_printf(xbt, dev->nodename, "event-channel", "%u",
-- 
1.7.3.4


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