xen/arm: alternative: Clean-up __apply_alternatives

This patch contains only renaming and comment update. There are no
functional changes:
    - Don't mix _start and _stext, they both point to the same address
    but the former makes more sense (we are mapping the Xen binary, not
    only the text section).
    - s/text_mfn/xen_mfn/ and s/text_order/xen_order/ to make clear that
    we map the Xen binary.
    - Mention about inittext as alternative may patch this section.
    - Use 1U instead of 1 in shift

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Julien Grall <julien.grall@arm.com>

xen/arch/arm/alternative.c

@@ -99,21 +99,21 @@ static int __apply_alternatives(const struct alt_region *region)
     const struct alt_instr *alt;
     const u32 *origptr, *replptr;
     u32 *writeptr, *writemap;
-    mfn_t text_mfn = _mfn(virt_to_mfn(_stext));
-    unsigned int text_order = get_order_from_bytes(_end - _start);
+    mfn_t xen_mfn = _mfn(virt_to_mfn(_start));
+    unsigned int xen_order = get_order_from_bytes(_end - _start);
 
     printk(XENLOG_INFO "alternatives: Patching kernel code\n");
 
     /*
-     * The text section is read-only. So re-map Xen to be able to patch
-     * the code.
+     * The text and inittext section are read-only. So re-map Xen to be
+     * able to patch the code.
      */
-    writemap = __vmap(&text_mfn, 1 << text_order, 1, 1, PAGE_HYPERVISOR,
+    writemap = __vmap(&xen_mfn, 1U << xen_order, 1, 1, PAGE_HYPERVISOR,
                       VMAP_DEFAULT);
     if ( !writemap )
     {
         printk(XENLOG_ERR "alternatives: Unable to map the text section (size %u)\n",
-               1 << text_order);
+               1 << xen_order);
         return -ENOMEM;
     }