[Qemu-devel] [PATCH] xenfb: map framebuffer read-only and handle unmap errors

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

The framebuffer is needlessly mapped (PROT_READ | PROT_WRITE), map it
PROT_READ instead.

The framebuffer is unmapped by replacing the framebuffer pages with
anonymous shared memory, calling mmap. Check for return errors and print
a warning.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
CC: Gerd Hoffmann <kraxel@redhat.com>
CC: Paolo Bonzini <pbonzini@redhat.com>
CC: Anthony Liguori <anthony@codemonkey.ws>
CC: phcoder@gmail.com

diff --git a/hw/display/xenfb.c b/hw/display/xenfb.c
index f0333a0..cb9d456 100644
--- a/hw/display/xenfb.c
+++ b/hw/display/xenfb.c
@@ -495,7 +495,7 @@ static int xenfb_map_fb(struct XenFB *xenfb)
     munmap(map, n_fbdirs * XC_PAGE_SIZE);
 
     xenfb->pixels = xc_map_foreign_pages(xen_xc, xenfb->c.xendev.dom,
-					 PROT_READ | PROT_WRITE, fbmfns, xenfb->fbpages);
+            PROT_READ, fbmfns, xenfb->fbpages);
     if (xenfb->pixels == NULL)
 	goto out;
 
@@ -903,6 +903,11 @@ static void fb_disconnect(struct XenDevice *xendev)
     fb->pixels = mmap(fb->pixels, fb->fbpages * XC_PAGE_SIZE,
                       PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANON,
                       -1, 0);
+    if (fb->pixels == MAP_FAILED) {
+        xen_be_printf(xendev, 0,
+                "Couldn't replace the framebuffer with anonymous memory errno=%d\n",
+                errno);
+    }
     common_unbind(&fb->c);
     fb->feature_update = 0;
     fb->bug_trigger    = 0;