[PATCH] x86/boot: Drop incorrect mapping at l2_xenmap[0]

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

It has been 4 years since the default load address changed from 1M to 2M, and
_stext ceased residing in l2_xenmap[0].  We should not be inserting an unused
mapping.

To ensure we don't create/remove mappings accidentally, loop from 0 and obey
_PAGE_PRESENT on all entries.

Fixes: 7ed93f3a0dff ("x86: change default load address from 1 MiB to 2 MiB")
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>

I ought to have spotted this in c/s 52975142d154 ("x86/boot: Create the
l2_xenmap[] mappings dynamically") too.
---
 xen/arch/x86/setup.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index da47cdea14a1..6f241048425c 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -1279,16 +1279,12 @@ 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));
-            /*
-             * Undo the temporary-hooking of the l1_directmap.  __2M_text_start
-             * is contained in this PTE.
-             */
+
             BUG_ON(using_2M_mapping() &&
                    l2_table_offset((unsigned long)_erodata) ==
                    l2_table_offset((unsigned long)_stext));
-            *pl2e++ = l2e_from_pfn(xen_phys_start >> PAGE_SHIFT,
-                                   PAGE_HYPERVISOR_RX | _PAGE_PSE);
-            for ( i = 1; i < L2_PAGETABLE_ENTRIES; i++, pl2e++ )
+
+            for ( i = 0; i < L2_PAGETABLE_ENTRIES; i++, pl2e++ )
             {
                 unsigned int flags;
 
-- 
2.11.0