xen: Use host-provided E820 map

Rather than simply using a flat memory map from Xen, use its provided
E820 map.  This allows the domain builder to tell the domain to reserve
space for more pages than those initially provided at domain-build time.

It also allows the host to specify holes in the address space (for
PCI-passthrough, for example).

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

1 files changed, 36 insertions, 2 deletions

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 328b00305426..dd2eb2a9303f 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -19,6 +19,7 @@
 
 #include <xen/page.h>
 #include <xen/interface/callback.h>
+#include <xen/interface/memory.h>
 #include <xen/interface/physdev.h>
 #include <xen/interface/memory.h>
 #include <xen/features.h>
@@ -107,13 +108,46 @@ static unsigned long __init xen_return_unused_memory(unsigned long max_pfn,
 
 char * __init xen_memory_setup(void)
 {
+        static struct e820entry map[E820MAX] __initdata;
+
         unsigned long max_pfn = xen_start_info->nr_pages;
+        unsigned long long mem_end;
+        int rc;
+        struct xen_memory_map memmap;
+        int i;
 
         max_pfn = min(MAX_DOMAIN_PAGES, max_pfn);
+        mem_end = PFN_PHYS(max_pfn);
+
+        memmap.nr_entries = E820MAX;
+        set_xen_guest_handle(memmap.buffer, map);
+
+        rc = HYPERVISOR_memory_op(XENMEM_memory_map, &memmap);
+        if (rc == -ENOSYS) {
+                memmap.nr_entries = 1;
+                map[0].addr = 0ULL;
+                map[0].size = mem_end;
+                /* 8MB slack (to balance backend allocations). */
+                map[0].size += 8ULL << 20;
+                map[0].type = E820_RAM;
+                rc = 0;
+        }
+        BUG_ON(rc);
 
         e820.nr_map = 0;
-
-        e820_add_region(0, PFN_PHYS((u64)max_pfn), E820_RAM);
+        for (i = 0; i < memmap.nr_entries; i++) {
+                unsigned long long end = map[i].addr + map[i].size;
+                if (map[i].type == E820_RAM) {
+                        if (map[i].addr > mem_end)
+                                continue;
+                        if (end > mem_end) {
+                                /* Truncate region to max_mem. */
+                                map[i].size -= end - mem_end;
+                        }
+                }
+                if (map[i].size > 0)
+                        e820_add_region(map[i].addr, map[i].size, map[i].type);
+        }
 
         /*
          * Even though this is normal, usable memory under Xen, reserve