[PATCH 10/15] x86/PVH: convert find_memory() to using a rangeset

[Jan Beulich <jbeulich@xxxxxxxx>]

Subsequently we will need to exclude a 2nd range here. To avoid
complicating the logic when it needs to cover two ranges, follow the
suggestion left in a code comment and convert to using a rangeset.

Suggested-by: Xenia Ragiadakou <xenia.ragiadakou@xxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
The Suggested-by: is based on the respective commit's S-o-b. I didn't go
hunt for whether this may have been suggested in review of that patch.

--- a/xen/arch/x86/hvm/dom0_build.c
+++ b/xen/arch/x86/hvm/dom0_build.c
@@ -518,14 +518,38 @@ static int __init pvh_populate_p2m(
 #undef MB1_PAGES
 }
 
+struct mem_info {
+    size_t size;
+    paddr_t addr;
+};
+
+static int cf_check __init _find_memory(
+    unsigned long s, unsigned long e, void *data)
+{
+    struct mem_info *info = data;
+
+    if ( e + 1 - s >= info->size )
+    {
+        info->addr = s;
+        return 1;
+    }
+
+    return 0;
+}
+
 static paddr_t __init find_memory(
     const struct domain *d, const struct elf_binary *elf, size_t size)
 {
-    paddr_t kernel_start = (paddr_t)elf->dest_base & PAGE_MASK;
-    paddr_t kernel_end = ROUNDUP((paddr_t)elf->dest_base + elf->dest_size,
-                                 PAGE_SIZE);
+    struct rangeset *ram = rangeset_new(NULL, NULL, 0);
+    struct mem_info info = {
+        .size = size,
+        .addr = INVALID_PADDR,
+    };
     unsigned int i;
 
+    if ( !ram )
+        return INVALID_PADDR;
+
     /*
      * The memory map is sorted and all RAM region starts are aligned to
      * page boundaries.
@@ -542,26 +566,22 @@ static paddr_t __init find_memory(
 
         ASSERT(IS_ALIGNED(start, PAGE_SIZE));
 
-        /*
-         * NB: Even better would be to use rangesets to determine a suitable
-         * range, in particular in case a kernel requests multiple heavily
-         * discontiguous regions (which right now we fold all into one big
-         * region).
-         */
-        if ( end <= kernel_start || start >= kernel_end )
-        {
-            /* No overlap, just check whether the region is large enough. */
-            if ( end - start >= size )
-                return start;
-        }
-        /* Deal with the kernel already being loaded in the region. */
-        else if ( kernel_start > start && kernel_start - start >= size )
-            return start;
-        else if ( kernel_end < end && end - kernel_end >= size )
-            return kernel_end;
+        if ( start < end &&
+             rangeset_add_range(ram, start, end - 1) != 0 )
+            return INVALID_PADDR;
     }
 
-    return INVALID_PADDR;
+    /* Remove the kernel range, rounded to page boundaries. */
+    if ( rangeset_remove_range(ram, (paddr_t)elf->dest_base & PAGE_MASK,
+                               ROUNDUP((paddr_t)elf->dest_base + 
elf->dest_size,
+                                       PAGE_SIZE) - 1) != 0 )
+        return INVALID_PADDR;
+
+    rangeset_report_ranges(ram, MB(1), -1, _find_memory, &info);
+
+    rangeset_destroy(ram);
+
+    return info.addr;
 }
 
 static bool __init check_load_address(