xen: fix UP setup of shared_info

We need to set up the shared_info pointer once we've mapped the real
shared_info into its fixmap slot.  That needs to happen once the general
pagetable setup has been done.  Previously, the UP shared_info was set
up one in xen_start_kernel, but that was left pointing to the dummy
shared info.  Unfortunately there's no really good place to do a later
setup of the shared_info in UP, so just do it once the pagetable setup
has been done.

[ Stable: needed in 2.6.24.x ]

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Stable Kernel <stable@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/xen/enlighten.c

@@ -103,6 +103,7 @@ static void __init xen_vcpu_setup(int cpu)
 	int err;
 	struct vcpu_info *vcpup;
 
+	BUG_ON(HYPERVISOR_shared_info == &dummy_shared_info);
 	per_cpu(xen_vcpu, cpu) = &HYPERVISOR_shared_info->vcpu_info[cpu];
 
 	if (!have_vcpu_info_placement)
@@ -805,33 +806,43 @@ static __init void xen_pagetable_setup_start(pgd_t *base)
 			  PFN_DOWN(__pa(xen_start_info->pt_base)));
 }
 
-static __init void xen_pagetable_setup_done(pgd_t *base)
+static __init void setup_shared_info(void)
 {
-	/* This will work as long as patching hasn't happened yet
-	   (which it hasn't) */
-	pv_mmu_ops.alloc_pt = xen_alloc_pt;
-	pv_mmu_ops.alloc_pd = xen_alloc_pd;
-	pv_mmu_ops.release_pt = xen_release_pt;
-	pv_mmu_ops.release_pd = xen_release_pt;
-	pv_mmu_ops.set_pte = xen_set_pte;
-
 	if (!xen_feature(XENFEAT_auto_translated_physmap)) {
+		unsigned long addr = fix_to_virt(FIX_PARAVIRT_BOOTMAP);
+
 		/*
 		 * Create a mapping for the shared info page.
 		 * Should be set_fixmap(), but shared_info is a machine
 		 * address with no corresponding pseudo-phys address.
 		 */
-		set_pte_mfn(fix_to_virt(FIX_PARAVIRT_BOOTMAP),
+		set_pte_mfn(addr,
 			    PFN_DOWN(xen_start_info->shared_info),
 			    PAGE_KERNEL);
 
-		HYPERVISOR_shared_info =
-			(struct shared_info *)fix_to_virt(FIX_PARAVIRT_BOOTMAP);
-
+		HYPERVISOR_shared_info = (struct shared_info *)addr;
 	} else
 		HYPERVISOR_shared_info =
 			(struct shared_info *)__va(xen_start_info->shared_info);
 
+#ifndef CONFIG_SMP
+	/* In UP this is as good a place as any to set up shared info */
+	xen_setup_vcpu_info_placement();
+#endif
+}
+
+static __init void xen_pagetable_setup_done(pgd_t *base)
+{
+	/* This will work as long as patching hasn't happened yet
+	   (which it hasn't) */
+	pv_mmu_ops.alloc_pt = xen_alloc_pt;
+	pv_mmu_ops.alloc_pd = xen_alloc_pd;
+	pv_mmu_ops.release_pt = xen_release_pt;
+	pv_mmu_ops.release_pd = xen_release_pt;
+	pv_mmu_ops.set_pte = xen_set_pte;
+
+	setup_shared_info();
+
 	/* Actually pin the pagetable down, but we can't set PG_pinned
 	   yet because the page structures don't exist yet. */
 	{
@@ -1182,15 +1193,9 @@ asmlinkage void __init xen_start_kernel(void)
 	x86_write_percpu(xen_cr3, __pa(pgd));
 	x86_write_percpu(xen_current_cr3, __pa(pgd));
 
-#ifdef CONFIG_SMP
 	/* Don't do the full vcpu_info placement stuff until we have a
-	   possible map. */
+	   possible map and a non-dummy shared_info. */
 	per_cpu(xen_vcpu, 0) = &HYPERVISOR_shared_info->vcpu_info[0];
-#else
-	/* May as well do it now, since there's no good time to call
-	   it later on UP. */
-	xen_setup_vcpu_info_placement();
-#endif
 
 	pv_info.kernel_rpl = 1;
 	if (xen_feature(XENFEAT_supervisor_mode_kernel))