pvgrub: fix crash when booting kernel with p2m list outside kernel mapping

When trying to boot a kernel with the p2m list not mapped by the
initial kernel mapping it can happen that pvgrub is failing as it is
keeping some page tables mapped.

Unmap the additional page tables created for the special p2m mapping
will avoid this failure.

Reported-by: Sven Koehler <sven.koehler@gmail.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>

stubdom/grub/kexec.c

@@ -347,6 +347,8 @@ void kexec(void *kernel, long kernel_size, void *module, long module_size, char
     /* Unmap libxc's projection of the boot page table */
     seg = xc_dom_seg_to_ptr(dom, &dom->pgtables_seg);
     munmap(seg, dom->pgtables_seg.vend - dom->pgtables_seg.vstart);
+    seg = xc_dom_seg_to_ptr(dom, &dom->p2m_seg);
+    munmap(seg, dom->p2m_seg.vend - dom->p2m_seg.vstart);
 
     /* Unmap day0 pages to avoid having a r/w mapping of the future page table */
     for (pfn = 0; pfn < allocated; pfn++)