xen/x86: Use memblock_reserve for sensitive areas.

instead of a big memblock_reserve. This way we can be more
selective in freeing regions (and it also makes it easier
to understand where is what).

[v1: Move the auto_translate_physmap to proper line]
[v2: Per Stefano suggestion add more comments]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

arch/x86/xen/enlighten.c

@@ -998,7 +998,54 @@ static int xen_write_msr_safe(unsigned int msr, unsigned low, unsigned high)
 
 	return ret;
 }
+/*
+ * If the MFN is not in the m2p (provided to us by the hypervisor) this
+ * function won't do anything. In practice this means that the XenBus
+ * MFN won't be available for the initial domain. */
+static void __init xen_reserve_mfn(unsigned long mfn)
+{
+	unsigned long pfn;
+
+	if (!mfn)
+		return;
+	pfn = mfn_to_pfn(mfn);
+	if (phys_to_machine_mapping_valid(pfn))
+		memblock_reserve(PFN_PHYS(pfn), PAGE_SIZE);
+}
+static void __init xen_reserve_internals(void)
+{
+	unsigned long size;
+
+	if (!xen_pv_domain())
+		return;
+
+	/* xen_start_info does not exist in the M2P, hence can't use
+	 * xen_reserve_mfn. */
+	memblock_reserve(__pa(xen_start_info), PAGE_SIZE);
+
+	xen_reserve_mfn(PFN_DOWN(xen_start_info->shared_info));
+	xen_reserve_mfn(xen_start_info->store_mfn);
 
+	if (!xen_initial_domain())
+		xen_reserve_mfn(xen_start_info->console.domU.mfn);
+
+	if (xen_feature(XENFEAT_auto_translated_physmap))
+		return;
+
+	/*
+	 * ALIGN up to compensate for the p2m_page pointing to an array that
+	 * can partially filled (look in xen_build_dynamic_phys_to_machine).
+	 */
+
+	size = PAGE_ALIGN(xen_start_info->nr_pages * sizeof(unsigned long));
+
+	/* We could use xen_reserve_mfn here, but would end up looping quite
+	 * a lot (and call memblock_reserve for each PAGE), so lets just use
+	 * the easy way and reserve it wholesale. */
+	memblock_reserve(__pa(xen_start_info->mfn_list), size);
+
+	/* The pagetables are reserved in mmu.c */
+}
 void xen_setup_shared_info(void)
 {
 	if (!xen_feature(XENFEAT_auto_translated_physmap)) {
@@ -1362,6 +1409,7 @@ asmlinkage void __init xen_start_kernel(void)
 	xen_raw_console_write("mapping kernel into physical memory\n");
 	pgd = xen_setup_kernel_pagetable(pgd, xen_start_info->nr_pages);
 
+	xen_reserve_internals();
 	/* Allocate and initialize top and mid mfn levels for p2m structure */
 	xen_build_mfn_list_list();
 

arch/x86/xen/p2m.c

@@ -388,6 +388,11 @@ void __init xen_build_dynamic_phys_to_machine(void)
 	}
 
 	m2p_override_init();
+
+	/* NOTE: We cannot call memblock_reserve here for the mfn_list as there
+	 * isn't enough pieces to make it work (for one - we are still using the
+	 * Xen provided pagetable). Do it later in xen_reserve_internals.
+	 */
 }
 
 unsigned long get_phys_to_machine(unsigned long pfn)

arch/x86/xen/setup.c

@@ -424,15 +424,6 @@ char * __init xen_memory_setup(void)
 	e820_add_region(ISA_START_ADDRESS, ISA_END_ADDRESS - ISA_START_ADDRESS,
 			E820_RESERVED);
 
-	/*
-	 * Reserve Xen bits:
-	 *  - mfn_list
-	 *  - xen_start_info
-	 * See comment above "struct start_info" in <xen/interface/xen.h>
-	 */
-	memblock_reserve(__pa(xen_start_info->mfn_list),
-			 xen_start_info->pt_base - xen_start_info->mfn_list);
-
 	sanitize_e820_map(e820.map, ARRAY_SIZE(e820.map), &e820.nr_map);
 
 	return "Xen";