accel/tcg: Introduce page_find_range_empty

Use the interval tree to locate an unused range in the VM.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230707204054.8792-17-richard.henderson@linaro.org>

accel/tcg/user-exec.c

@@ -605,6 +605,47 @@ bool page_check_range_empty(target_ulong start, target_ulong last)
     return pageflags_find(start, last) == NULL;
 }
 
+target_ulong page_find_range_empty(target_ulong min, target_ulong max,
+                                   target_ulong len, target_ulong align)
+{
+    target_ulong len_m1, align_m1;
+
+    assert(min <= max);
+    assert(max <= GUEST_ADDR_MAX);
+    assert(len != 0);
+    assert(is_power_of_2(align));
+    assert_memory_lock();
+
+    len_m1 = len - 1;
+    align_m1 = align - 1;
+
+    /* Iteratively narrow the search region. */
+    while (1) {
+        PageFlagsNode *p;
+
+        /* Align min and double-check there's enough space remaining. */
+        min = (min + align_m1) & ~align_m1;
+        if (min > max) {
+            return -1;
+        }
+        if (len_m1 > max - min) {
+            return -1;
+        }
+
+        p = pageflags_find(min, min + len_m1);
+        if (p == NULL) {
+            /* Found! */
+            return min;
+        }
+        if (max <= p->itree.last) {
+            /* Existing allocation fills the remainder of the search region. */
+            return -1;
+        }
+        /* Skip across existing allocation. */
+        min = p->itree.last + 1;
+    }
+}
+
 void page_protect(tb_page_addr_t address)
 {
     PageFlagsNode *p;

include/exec/cpu-all.h

@@ -236,6 +236,21 @@ int page_check_range(target_ulong start, target_ulong len, int flags);
  */
 bool page_check_range_empty(target_ulong start, target_ulong last);
 
+/**
+ * page_find_range_empty
+ * @min: first byte of search range
+ * @max: last byte of search range
+ * @len: size of the hole required
+ * @align: alignment of the hole required (power of 2)
+ *
+ * If there is a range [x, x+@len) within [@min, @max] such that
+ * x % @align == 0, then return x.  Otherwise return -1.
+ * The memory lock must be held, as the caller will want to ensure
+ * the returned range stays empty until a new mapping can be installed.
+ */
+target_ulong page_find_range_empty(target_ulong min, target_ulong max,
+                                   target_ulong len, target_ulong align);
+
 /**
  * page_get_target_data(address)
  * @address: guest virtual address