[PATCH 2/2] x86: drop high compat r/o M2P table address range

[Jan Beulich <jbeulich@xxxxxxxx>]

Now that we don't properly hook things up into the page tables anymore
we also don't need to set aside an address range. Drop it, using
compat_idle_pg_table_l2[] simply (explicitly) from slot 0.

While doing the re-arrangement, which is accompanied by the dropping or
replacing of some local variables, restrict the scopes of some further
ones at the same time.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
TBD: With the changed usage perhaps we want to also rename
     compat_idle_pg_table_l2[] (to e.g. compat_idle_l2_entries[])?

--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -1454,8 +1454,7 @@ static bool pae_xen_mappings_check(const
 void init_xen_pae_l2_slots(l2_pgentry_t *l2t, const struct domain *d)
 {
     memcpy(&l2t[COMPAT_L2_PAGETABLE_FIRST_XEN_SLOT(d)],
-           &compat_idle_pg_table_l2[
-               l2_table_offset(HIRO_COMPAT_MPT_VIRT_START)],
+           compat_idle_pg_table_l2,
            COMPAT_L2_PAGETABLE_XEN_SLOTS(d) * sizeof(*l2t));
 }
 
--- a/xen/arch/x86/x86_64/mm.c
+++ b/xen/arch/x86/x86_64/mm.c
@@ -217,9 +217,7 @@ static int share_hotadd_m2p_table(struct
 
 static void destroy_compat_m2p_mapping(struct mem_hotadd_info *info)
 {
-    unsigned long i, va, rwva, pt_pfn;
-    unsigned long smap = info->spfn, emap = info->spfn;
-    l2_pgentry_t *l2_ro_mpt = compat_idle_pg_table_l2;
+    unsigned long i, smap = info->spfn, emap = info->spfn;
 
     if ( smap > ((RDWR_COMPAT_MPT_VIRT_END - RDWR_COMPAT_MPT_VIRT_START) >> 2) 
)
         return;
@@ -229,18 +227,19 @@ static void destroy_compat_m2p_mapping(s
 
     for ( i = smap; i < emap; )
     {
-        va = HIRO_COMPAT_MPT_VIRT_START +
-              i * sizeof(*compat_machine_to_phys_mapping);
-        rwva = RDWR_COMPAT_MPT_VIRT_START +
-             i * sizeof(*compat_machine_to_phys_mapping);
-        if ( l2e_get_flags(l2_ro_mpt[l2_table_offset(va)]) & _PAGE_PRESENT )
+        unsigned int off = i * sizeof(*compat_machine_to_phys_mapping);
+        l2_pgentry_t *pl2e = compat_idle_pg_table_l2 + l2_table_offset(off);
+
+        if ( l2e_get_flags(*pl2e) & _PAGE_PRESENT )
         {
-            pt_pfn = l2e_get_pfn(l2_ro_mpt[l2_table_offset(va)]);
+            unsigned long pt_pfn = l2e_get_pfn(*pl2e);
+
             if ( hotadd_mem_valid(pt_pfn, info) )
             {
-                destroy_xen_mappings(rwva, rwva +
-                        (1UL << L2_PAGETABLE_SHIFT));
-                l2e_write(&l2_ro_mpt[l2_table_offset(va)], l2e_empty());
+                unsigned long rwva = RDWR_COMPAT_MPT_VIRT_START + off;
+
+                destroy_xen_mappings(rwva, rwva + (1UL << L2_PAGETABLE_SHIFT));
+                l2e_write(pl2e, l2e_empty());
             }
         }
 
@@ -312,10 +311,9 @@ static void destroy_m2p_mapping(struct m
  */
 static int setup_compat_m2p_table(struct mem_hotadd_info *info)
 {
-    unsigned long i, va, smap, emap, rwva, epfn = info->epfn;
+    unsigned long i, smap, emap, epfn = info->epfn;
     mfn_t mfn;
     unsigned int n;
-    l2_pgentry_t *l2_ro_mpt = NULL;
     int err = 0;
 
     smap = info->spfn & (~((1UL << (L2_PAGETABLE_SHIFT - 2)) -1));
@@ -333,8 +331,6 @@ static int setup_compat_m2p_table(struct
     emap = ( (epfn + ((1UL << (L2_PAGETABLE_SHIFT - 2)) - 1 )) &
                 ~((1UL << (L2_PAGETABLE_SHIFT - 2)) - 1) );
 
-    l2_ro_mpt = compat_idle_pg_table_l2;
-
 #define MFN(x) (((x) << L2_PAGETABLE_SHIFT) / sizeof(unsigned int))
 #define CNT ((sizeof(*frame_table) & -sizeof(*frame_table)) / \
              sizeof(*compat_machine_to_phys_mapping))
@@ -343,13 +339,11 @@ static int setup_compat_m2p_table(struct
 
     for ( i = smap; i < emap; i += (1UL << (L2_PAGETABLE_SHIFT - 2)) )
     {
-        va = HIRO_COMPAT_MPT_VIRT_START +
-              i * sizeof(*compat_machine_to_phys_mapping);
-
-        rwva = RDWR_COMPAT_MPT_VIRT_START +
-                i * sizeof(*compat_machine_to_phys_mapping);
+        unsigned int off = i * sizeof(*compat_machine_to_phys_mapping);
+        l2_pgentry_t *pl2e = compat_idle_pg_table_l2 + l2_table_offset(off);
+        unsigned long rwva = RDWR_COMPAT_MPT_VIRT_START + off;
 
-        if (l2e_get_flags(l2_ro_mpt[l2_table_offset(va)]) & _PAGE_PRESENT)
+        if ( l2e_get_flags(*pl2e) & _PAGE_PRESENT )
             continue;
 
         for ( n = 0; n < CNT; ++n)
@@ -366,8 +360,7 @@ static int setup_compat_m2p_table(struct
         /* Fill with INVALID_M2P_ENTRY. */
         memset((void *)rwva, 0xFF, 1UL << L2_PAGETABLE_SHIFT);
         /* NB. Cannot be GLOBAL as the ptes get copied into per-VM space. */
-        l2e_write(&l2_ro_mpt[l2_table_offset(va)],
-                  l2e_from_mfn(mfn, _PAGE_PSE|_PAGE_PRESENT));
+        l2e_write(pl2e, l2e_from_mfn(mfn, _PAGE_PSE|_PAGE_PRESENT));
     }
 #undef CNT
 #undef MFN
@@ -616,7 +609,6 @@ void __init paging_init(void)
         goto nomem;
     compat_idle_pg_table_l2 = l2_ro_mpt;
     clear_page(l2_ro_mpt);
-    l2_ro_mpt += l2_table_offset(HIRO_COMPAT_MPT_VIRT_START);
     /* Allocate and map the compatibility mode machine-to-phys table. */
     mpt_size = (mpt_size >> 1) + (1UL << (L2_PAGETABLE_SHIFT - 1));
     if ( mpt_size > RDWR_COMPAT_MPT_VIRT_END - RDWR_COMPAT_MPT_VIRT_START )
--- a/xen/include/asm-x86/config.h
+++ b/xen/include/asm-x86/config.h
@@ -215,11 +215,8 @@ extern unsigned char boot_edid_info[128]
 /* Slot 261: compatibility machine-to-phys conversion table (1GB). */
 #define RDWR_COMPAT_MPT_VIRT_START VMAP_VIRT_END
 #define RDWR_COMPAT_MPT_VIRT_END (RDWR_COMPAT_MPT_VIRT_START + GB(1))
-/* Slot 261: high read-only compat machine-to-phys conversion table (1GB). */
-#define HIRO_COMPAT_MPT_VIRT_START RDWR_COMPAT_MPT_VIRT_END
-#define HIRO_COMPAT_MPT_VIRT_END (HIRO_COMPAT_MPT_VIRT_START + GB(1))
 /* Slot 261: xen text, static data, bss, per-cpu stubs and executable fixmap 
(1GB). */
-#define XEN_VIRT_START          (HIRO_COMPAT_MPT_VIRT_END)
+#define XEN_VIRT_START          RDWR_COMPAT_MPT_VIRT_END
 #define XEN_VIRT_END            (XEN_VIRT_START + GB(1))
 
 #ifndef CONFIG_BIGMEM