xen/mmu: Call xen_cleanhighmap() with 4MB aligned for page tables mapping

When bootup a PVM guest with large memory(Ex.240GB), XEN provided initial
mapping overlaps with kernel module virtual space. When mapping in this space
is cleared by xen_cleanhighmap(), in certain case there could be an 2MB mapping
left. This is due to XEN initialize 4MB aligned mapping but xen_cleanhighmap()
finish at 2MB boundary.

When module loading is just on top of the 2MB space, got below warning:

WARNING: at mm/vmalloc.c:106 vmap_pte_range+0x14e/0x190()
Call Trace:
 [<ffffffff81117083>] warn_alloc_failed+0xf3/0x160
 [<ffffffff81146022>] __vmalloc_area_node+0x182/0x1c0
 [<ffffffff810ac91e>] ? module_alloc_update_bounds+0x1e/0x80
 [<ffffffff81145df7>] __vmalloc_node_range+0xa7/0x110
 [<ffffffff810ac91e>] ? module_alloc_update_bounds+0x1e/0x80
 [<ffffffff8103ca54>] module_alloc+0x64/0x70
 [<ffffffff810ac91e>] ? module_alloc_update_bounds+0x1e/0x80
 [<ffffffff810ac91e>] module_alloc_update_bounds+0x1e/0x80
 [<ffffffff810ac9a7>] move_module+0x27/0x150
 [<ffffffff810aefa0>] layout_and_allocate+0x120/0x1b0
 [<ffffffff810af0a8>] load_module+0x78/0x640
 [<ffffffff811ff90b>] ? security_file_permission+0x8b/0x90
 [<ffffffff810af6d2>] sys_init_module+0x62/0x1e0
 [<ffffffff815154c2>] system_call_fastpath+0x16/0x1b

Then the mapping of 2MB is cleared, finally oops when the page in that space is
accessed.

BUG: unable to handle kernel paging request at ffff880022600000
IP: [<ffffffff81260877>] clear_page_c_e+0x7/0x10
PGD 1788067 PUD 178c067 PMD 22434067 PTE 0
Oops: 0002 [#1] SMP
Call Trace:
 [<ffffffff81116ef7>] ? prep_new_page+0x127/0x1c0
 [<ffffffff81117d42>] get_page_from_freelist+0x1e2/0x550
 [<ffffffff81133010>] ? ii_iovec_copy_to_user+0x90/0x140
 [<ffffffff81119c9d>] __alloc_pages_nodemask+0x12d/0x230
 [<ffffffff81155516>] alloc_pages_vma+0xc6/0x1a0
 [<ffffffff81006ffd>] ? pte_mfn_to_pfn+0x7d/0x100
 [<ffffffff81134cfb>] do_anonymous_page+0x16b/0x350
 [<ffffffff81139c34>] handle_pte_fault+0x1e4/0x200
 [<ffffffff8100712e>] ? xen_pmd_val+0xe/0x10
 [<ffffffff810052c9>] ? __raw_callee_save_xen_pmd_val+0x11/0x1e
 [<ffffffff81139dab>] handle_mm_fault+0x15b/0x270
 [<ffffffff81510c10>] do_page_fault+0x140/0x470
 [<ffffffff8150d7d5>] page_fault+0x25/0x30

Call xen_cleanhighmap() with 4MB aligned for page tables mapping to fix it.
The unnecessory call of xen_cleanhighmap() in DEBUG mode is also removed.

-v2: add comment about XEN alignment from Juergen.

References: https://lists.xen.org/archives/html/xen-devel/2012-07/msg01562.html
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Reviewed-by: Juergen Gross <jgross@suse.com>

[boris: added 'xen/mmu' tag to commit subject]
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

arch/x86/xen/mmu_pv.c

@@ -1238,21 +1238,16 @@ static void __init xen_pagetable_cleanhighmap(void)
 	 * from _brk_limit way up to the max_pfn_mapped (which is the end of
 	 * the ramdisk). We continue on, erasing PMD entries that point to page
 	 * tables - do note that they are accessible at this stage via __va.
-	 * For good measure we also round up to the PMD - which means that if
+	 * As Xen is aligning the memory end to a 4MB boundary, for good
+	 * measure we also round up to PMD_SIZE * 2 - which means that if
 	 * anybody is using __ka address to the initial boot-stack - and try
 	 * to use it - they are going to crash. The xen_start_info has been
 	 * taken care of already in xen_setup_kernel_pagetable. */
 	addr = xen_start_info->pt_base;
-	size = roundup(xen_start_info->nr_pt_frames * PAGE_SIZE, PMD_SIZE);
+	size = xen_start_info->nr_pt_frames * PAGE_SIZE;
 
-	xen_cleanhighmap(addr, addr + size);
+	xen_cleanhighmap(addr, roundup(addr + size, PMD_SIZE * 2));
 	xen_start_info->pt_base = (unsigned long)__va(__pa(xen_start_info->pt_base));
-#ifdef DEBUG
-	/* This is superfluous and is not necessary, but you know what
-	 * lets do it. The MODULES_VADDR -> MODULES_END should be clear of
-	 * anything at this stage. */
-	xen_cleanhighmap(MODULES_VADDR, roundup(MODULES_VADDR, PUD_SIZE) - 1);
-#endif
 }
 #endif