[patch] kexec: minor xen tweaks

[Gerd Hoffmann <kraxel@suse.de>]

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  Hi,

The patch below makes two minor modifications to the xen kernel:

First it adds a printk when trying to switch page tables via idle page
table (happens when the new cr3 page table tree itself is valid, but
hasn't the old page table pages mapped read-only).  That helps alot when
trying to find the reason of error messages with verbose=y builds ;)

Second it allows the user baseptr being reset to 0 (unused) on x86_64,
which is needed for domU kexec.

please apply,

  Gerd

-- 
Gerd Hoffmann <kraxel@suse.de>
http://www.suse.de/~kraxel/julika-dora.jpeg

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Signed-off-by: Gerd Hoffmann <kraxel@suse.de>
diff -r befab551b0e1 xen/arch/x86/mm.c
--- a/xen/arch/x86/mm.c	Sun Aug 13 09:44:07 2006 +0100
+++ b/xen/arch/x86/mm.c	Mon Aug 14 12:49:11 2006 +0200
@@ -1763,6 +1763,7 @@ int new_guest_cr3(unsigned long mfn)
         if ( unlikely(!okay) )
         {
             /* Switch to idle pagetable: this VCPU has no active p.t. now. */
+            MEM_LOG("New baseptr %lx: slow path via idle pagetables", mfn);
             old_base_mfn = pagetable_get_pfn(v->arch.guest_table);
             v->arch.guest_table = pagetable_null();
             update_pagetables(v);
@@ -2046,8 +2047,10 @@ int do_mmuext_op(
         
 #ifdef __x86_64__
         case MMUEXT_NEW_USER_BASEPTR:
-            okay = get_page_and_type_from_pagenr(
-                mfn, PGT_root_page_table, d);
+            okay = 1;
+            if (likely(mfn != 0))
+                okay = get_page_and_type_from_pagenr(
+                    mfn, PGT_root_page_table, d);
             if ( unlikely(!okay) )
             {
                 MEM_LOG("Error while installing new mfn %lx", mfn);

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