[Xen-devel] [PATCH v3] x86/dom0: add extra RAM regions as UNUSABLE for PVH memory map

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

When running as PVH Dom0 the native memory map is used in order to
craft a tailored memory map for Dom0 taking into account it's memory
limit.

Dom0 memory is always going to be smaller than the total amount
of memory present on the host, so in order to prevent Dom0 from
relocating PCI BARs over RAM regions mark all the RAM regions not
available to Dom0 as UNUSABLE in the memory map.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Changes since v2:
 - This time really replace RESERVED with UNUSABLE.

Changes since v1:
 - Report the ranges as UNUSABLE instead of RESERVED.
---
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
---
NB: I haven't seen any system where Dom0 would relocate the BARs over
RAM regions, but AFAICT given the current memory map provided to Dom0
this is a possibility that should be avoided.
---
 xen/arch/x86/hvm/dom0_build.c | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/xen/arch/x86/hvm/dom0_build.c b/xen/arch/x86/hvm/dom0_build.c
index b237508072..e2b5d48e03 100644
--- a/xen/arch/x86/hvm/dom0_build.c
+++ b/xen/arch/x86/hvm/dom0_build.c
@@ -314,8 +314,10 @@ static __init void pvh_setup_e820(struct domain *d, 
unsigned long nr_pages)
 
     /*
      * Craft the e820 memory map for Dom0 based on the hardware e820 map.
+     * Add an extra entry in case we have to split a RAM entry into a RAM and a
+     * UNUSABLE one in order to truncate it.
      */
-    d->arch.e820 = xzalloc_array(struct e820entry, e820.nr_map);
+    d->arch.e820 = xzalloc_array(struct e820entry, e820.nr_map + 1);
     if ( !d->arch.e820 )
         panic("Unable to allocate memory for Dom0 e820 map");
     entry_guest = d->arch.e820;
@@ -323,19 +325,20 @@ static __init void pvh_setup_e820(struct domain *d, 
unsigned long nr_pages)
     /* Clamp e820 memory map to match the memory assigned to Dom0 */
     for ( i = 0, entry = e820.map; i < e820.nr_map; i++, entry++ )
     {
+        *entry_guest = *entry;
+
         if ( entry->type != E820_RAM )
-        {
-            *entry_guest = *entry;
             goto next;
-        }
 
         if ( nr_pages == cur_pages )
         {
             /*
-             * We already have all the assigned memory,
-             * skip this entry
+             * We already have all the requested memory, turn this RAM region
+             * into a UNUSABLE region in order to prevent Dom0 from placing
+             * BARs in this area.
              */
-            continue;
+            entry_guest->type = E820_UNUSABLE;
+            goto next;
         }
 
         /*
@@ -358,6 +361,12 @@ static __init void pvh_setup_e820(struct domain *d, 
unsigned long nr_pages)
         {
             /* Truncate region */
             entry_guest->size = (nr_pages - cur_pages) << PAGE_SHIFT;
+            /* Add the remaining of the RAM region as UNUSABLE. */
+            entry_guest++;
+            d->arch.nr_e820++;
+            entry_guest->type = E820_UNUSABLE;
+            entry_guest->addr = start + ((nr_pages - cur_pages) << PAGE_SHIFT);
+            entry_guest->size = end - entry_guest->addr;
             cur_pages = nr_pages;
         }
         else
@@ -367,9 +376,9 @@ static __init void pvh_setup_e820(struct domain *d, 
unsigned long nr_pages)
  next:
         d->arch.nr_e820++;
         entry_guest++;
+        ASSERT(d->arch.nr_e820 <= e820.nr_map + 1);
     }
     ASSERT(cur_pages == nr_pages);
-    ASSERT(d->arch.nr_e820 <= e820.nr_map);
 }
 
 static int __init pvh_setup_p2m(struct domain *d)
-- 
2.17.0


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