[xen staging] Revert "x86/mm: split unmapping and marking-as-I/O in arch_init_memory()"

[patchbot@xxxxxxx]

commit 22c2cca55280a11d2a1849137eb146830e606e76
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Aug 19 11:00:26 2025 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Aug 19 11:00:26 2025 +0200

    Revert "x86/mm: split unmapping and marking-as-I/O in arch_init_memory()"
    
    This reverts commit 248096b113fefd36260afb06a2520781ec37f9e8. This was a
    stale version of the patch, and thus also not what was ack-ed.
---
 xen/arch/x86/mm.c | 63 ++++++++++++++-----------------------------------------
 1 file changed, 16 insertions(+), 47 deletions(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 9ca3469a78..e7fd56c7ce 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -275,6 +275,8 @@ static void __init assign_io_page(struct page_info *page)
 
 void __init arch_init_memory(void)
 {
+    unsigned long i, pfn, rstart_pfn, rend_pfn, iostart_pfn, ioend_pfn;
+
     /*
      * Basic guest-accessible flags:
      *   PRESENT, R/W, USER, A/D, AVAIL[0,1,2], AVAIL_HIGH, NX (if available).
@@ -290,55 +292,12 @@ void __init arch_init_memory(void)
      * case the low 1MB.
      */
     BUG_ON(pvh_boot && trampoline_phys != 0x1000);
-    for ( unsigned int i = 0; i < MB(1) >> PAGE_SHIFT; i++ )
+    for ( i = 0; i < 0x100; i++ )
         assign_io_page(mfn_to_page(_mfn(i)));
 
-    /*
-     * Any areas not specified as RAM by the e820 map want to have no mappings.
-     * We may have established some by mapping more than necessary in head.S,
-     * due to the use of super-pages there.
-     */
-    for ( unsigned long i = 0, pfn = 0,
-                        rlimit_pfn = PFN_DOWN(PAGE_ALIGN_2M(__pa(_end)));
-          pfn < rlimit_pfn; i++ )
+    /* Any areas not specified as RAM by the e820 map are considered I/O. */
+    for ( i = 0, pfn = 0; pfn < max_page; i++ )
     {
-        unsigned long rstart_pfn, rend_pfn, start_pfn;
-
-        while ( i < e820.nr_map &&
-                e820.map[i].type != E820_RAM )
-            i++;
-
-        if ( i >= e820.nr_map )
-        {
-            /* No more RAM regions: Unmap right to upper boundary. */
-            rstart_pfn = rend_pfn = rlimit_pfn;
-        }
-        else
-        {
-            /* Unmap just up as far as next RAM region. */
-            rstart_pfn = min(rlimit_pfn, PFN_UP(e820.map[i].addr));
-            rend_pfn   = max(rstart_pfn,
-                             PFN_DOWN(e820.map[i].addr + e820.map[i].size));
-        }
-
-        /* NB: _start is already 2Mb-aligned. */
-        start_pfn = max(pfn, PFN_DOWN(__pa(_start)));
-        if ( start_pfn < rstart_pfn )
-            destroy_xen_mappings((unsigned long)mfn_to_virt(start_pfn),
-                                 (unsigned long)mfn_to_virt(rstart_pfn));
-
-        /* Skip the RAM region. */
-        pfn = rend_pfn;
-    }
-
-    /*
-     * Any areas not specified as RAM or UNUSABLE by the e820 map are
-     * considered I/O.
-     */
-    for ( unsigned long i = 0, pfn = 0; pfn < max_page; i++ )
-    {
-        unsigned long rstart_pfn, rend_pfn;
-
         while ( (i < e820.nr_map) &&
                 (e820.map[i].type != E820_RAM) &&
                 (e820.map[i].type != E820_UNUSABLE) )
@@ -358,6 +317,17 @@ void __init arch_init_memory(void)
                                PFN_DOWN(e820.map[i].addr + e820.map[i].size));
         }
 
+        /*
+         * Make sure any Xen mappings of RAM holes above 1MB are blown away.
+         * In particular this ensures that RAM holes are respected even in
+         * the statically-initialised 1-16MB mapping area.
+         */
+        iostart_pfn = max_t(unsigned long, pfn, 1UL << (20 - PAGE_SHIFT));
+        ioend_pfn = min(rstart_pfn, 16UL << (20 - PAGE_SHIFT));
+        if ( iostart_pfn < ioend_pfn )
+            destroy_xen_mappings((unsigned long)mfn_to_virt(iostart_pfn),
+                                 (unsigned long)mfn_to_virt(ioend_pfn));
+
         /* Mark as I/O up to next RAM region. */
         for ( ; pfn < rstart_pfn; pfn++ )
         {
@@ -395,7 +365,6 @@ void __init arch_init_memory(void)
                     const l3_pgentry_t *l3idle = map_l3t_from_l4e(
                             idle_pg_table[l4_table_offset(split_va)]);
                     l3_pgentry_t *l3tab = map_domain_page(l3mfn);
-                    unsigned int i;
 
                     for ( i = 0; i < l3_table_offset(split_va); ++i )
                         l3tab[i] = l3idle[i];
--
generated by git-patchbot for /home/xen/git/xen.git#staging