[Xen-devel] [PATCH] [RFC] xen: Fix memory hotplug end limit test for updating compat M2P table

[Malcolm Crossley <malcolm.crossley@xxxxxxxxxx>]

The memory hotplug code was masking the hotplugged memory start address and 
comparing to a shifted version of COMPAT MPT size but not doing the same for 
the end address.
This patch applies the same shifting and masking to the end address and 
reapplies the mask if the end address has been clamped.

diff -r 274e5accd62d -r 8470671d407f xen/arch/x86/x86_64/mm.c
--- a/xen/arch/x86/x86_64/mm.c
+++ b/xen/arch/x86/x86_64/mm.c
@@ -446,6 +446,8 @@ static int setup_compat_m2p_table(struct
     int err = 0;
 
     smap = info->spfn & (~((1UL << (L2_PAGETABLE_SHIFT - 2)) -1));
+    emap = ( (epfn + ((1UL << (L2_PAGETABLE_SHIFT - 2)) - 1 )) &
+                ~((1UL << (L2_PAGETABLE_SHIFT - 2)) - 1) );
 
     /*
      * Notice: For hot-added memory, only range below m2p_compat_vstart
@@ -454,11 +456,11 @@ static int setup_compat_m2p_table(struct
     if   ((smap > ((RDWR_COMPAT_MPT_VIRT_END - RDWR_COMPAT_MPT_VIRT_START) >> 
2)) )
         return 0;
 
-    if (epfn > (RDWR_COMPAT_MPT_VIRT_END - RDWR_COMPAT_MPT_VIRT_START))
-        epfn = (RDWR_COMPAT_MPT_VIRT_END - RDWR_COMPAT_MPT_VIRT_START) >> 2;
-
-    emap = ( (epfn + ((1UL << (L2_PAGETABLE_SHIFT - 2)) - 1 )) &
-                ~((1UL << (L2_PAGETABLE_SHIFT - 2)) - 1) );
+    if (emap > ((RDWR_COMPAT_MPT_VIRT_END - RDWR_COMPAT_MPT_VIRT_START) >> 2))
+    {
+        emap = (RDWR_COMPAT_MPT_VIRT_END - RDWR_COMPAT_MPT_VIRT_START) >> 2;
+       emap = emap & ~((1UL << (L2_PAGETABLE_SHIFT - 2)) - 1);
+    }
 
     va = HIRO_COMPAT_MPT_VIRT_START +
          smap * sizeof(*compat_machine_to_phys_mapping);

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