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>

1 files changed, 41 insertions, 0 deletions

diff --git a/accel/tcg/user-exec.c b/accel/tcg/user-exec.c
index ab684a3ea2..e4f9563730 100644
--- a/accel/tcg/user-exec.c
+++ b/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;