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



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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