[xen staging] x86/boot: Better describe the pagetable relocation loops

[patchbot@xxxxxxx]

commit 3099ff3ce15481b4f1536470cb87ac0ebf82b7bb
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Nov 29 19:19:43 2021 +0000
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Thu Dec 2 20:02:55 2021 +0000

    x86/boot: Better describe the pagetable relocation loops
    
    The first loop relocates all reachable non-leaf entries in idle_pg_table[],
    which includes l2_xenmap[511]'s reference to l1_fixmap_x[].
    
    The second loop relocates only leaf mappings in l2_xenmap[], so update the
    skip condition to be opposite to the first loop.
    
    No functional change.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/setup.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 6f24104842..495b4b7d51 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -1245,7 +1245,7 @@ void __init noreturn __start_xen(unsigned long mbi_p)
             barrier();
             move_memory(e, XEN_IMG_OFFSET, _end - _start, 1);
 
-            /* Walk initial pagetables, relocating page directory entries. */
+            /* Walk idle_pg_table, relocating non-leaf entries. */
             pl4e = __va(__pa(idle_pg_table));
             for ( i = 0 ; i < L4_PAGETABLE_ENTRIES; i++, pl4e++ )
             {
@@ -1277,18 +1277,18 @@ void __init noreturn __start_xen(unsigned long mbi_p)
                 }
             }
 
-            /* The only data mappings to be relocated are in the Xen area. */
-            pl2e = __va(__pa(l2_xenmap));
-
             BUG_ON(using_2M_mapping() &&
                    l2_table_offset((unsigned long)_erodata) ==
                    l2_table_offset((unsigned long)_stext));
 
+            /* Walk l2_xenmap[], relocating 2M superpage leaves. */
+            pl2e = __va(__pa(l2_xenmap));
             for ( i = 0; i < L2_PAGETABLE_ENTRIES; i++, pl2e++ )
             {
                 unsigned int flags;
 
                 if ( !(l2e_get_flags(*pl2e) & _PAGE_PRESENT) ||
+                     !(l2e_get_flags(*pl2e) & _PAGE_PSE) ||
                      (l2e_get_pfn(*pl2e) >= pte_update_limit) )
                     continue;
 
--
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