From f88f3ac90f9e98333abf91f23c8547a428cd90fa Mon Sep 17 00:00:00 2001
From: Richard Henderson <richard.henderson@linaro.org>
Date: Wed, 5 Oct 2022 16:22:16 -0700
Subject: [PATCH] accel/tcg: Use interval tree for TARGET_PAGE_DATA_SIZE
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Continue weaning user-only away from PageDesc.

Use an interval tree to record target data.
Chunk the data, to minimize allocation overhead.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 accel/tcg/internal.h  |  1 -
 accel/tcg/user-exec.c | 99 ++++++++++++++++++++++++++++++++-----------
 2 files changed, 74 insertions(+), 26 deletions(-)

diff --git a/accel/tcg/internal.h b/accel/tcg/internal.h
index bf1bf62e2a..0f91ee939c 100644
--- a/accel/tcg/internal.h
+++ b/accel/tcg/internal.h
@@ -26,7 +26,6 @@
 typedef struct PageDesc {
 #ifdef CONFIG_USER_ONLY
     unsigned long flags;
-    void *target_data;
 #else
     QemuSpin lock;
     /* list of TBs intersecting this ram page */
diff --git a/accel/tcg/user-exec.c b/accel/tcg/user-exec.c
index fb7d6ee9e9..42a04bdb21 100644
--- a/accel/tcg/user-exec.c
+++ b/accel/tcg/user-exec.c
@@ -210,47 +210,96 @@ tb_page_addr_t get_page_addr_code_hostp(CPUArchState *env, target_ulong addr,
     return addr;
 }
 
+#ifdef TARGET_PAGE_DATA_SIZE
+/*
+ * Allocate chunks of target data together.  For the only current user,
+ * if we allocate one hunk per page, we have overhead of 40/128 or 40%.
+ * Therefore, allocate memory for 64 pages at a time for overhead < 1%.
+ */
+#define TPD_PAGES  64
+#define TBD_MASK   (TARGET_PAGE_MASK * TPD_PAGES)
+
+typedef struct TargetPageDataNode {
+    IntervalTreeNode itree;
+    char data[TPD_PAGES][TARGET_PAGE_DATA_SIZE] __attribute__((aligned));
+} TargetPageDataNode;
+
+static IntervalTreeRoot targetdata_root;
+
 void page_reset_target_data(target_ulong start, target_ulong end)
 {
-#ifdef TARGET_PAGE_DATA_SIZE
-    target_ulong addr, len;
+    IntervalTreeNode *n, *next;
+    target_ulong last;
 
-    /*
-     * This function should never be called with addresses outside the
-     * guest address space.  If this assert fires, it probably indicates
-     * a missing call to h2g_valid.
-     */
-    assert(end - 1 <= GUEST_ADDR_MAX);
-    assert(start < end);
     assert_memory_lock();
 
     start = start & TARGET_PAGE_MASK;
-    end = TARGET_PAGE_ALIGN(end);
+    last = TARGET_PAGE_ALIGN(end) - 1;
 
-    for (addr = start, len = end - start;
-         len != 0;
-         len -= TARGET_PAGE_SIZE, addr += TARGET_PAGE_SIZE) {
-        PageDesc *p = page_find_alloc(addr >> TARGET_PAGE_BITS, 1);
+    for (n = interval_tree_iter_first(&targetdata_root, start, last),
+         next = n ? interval_tree_iter_next(n, start, last) : NULL;
+         n != NULL;
+         n = next,
+         next = next ? interval_tree_iter_next(n, start, last) : NULL) {
+        target_ulong n_start, n_last, p_ofs, p_len;
+        TargetPageDataNode *t;
 
-        g_free(p->target_data);
-        p->target_data = NULL;
+        if (n->start >= start && n->last <= last) {
+            interval_tree_remove(n, &targetdata_root);
+            g_free(n);
+            continue;
+        }
+
+        if (n->start < start) {
+            n_start = start;
+            p_ofs = (start - n->start) >> TARGET_PAGE_BITS;
+        } else {
+            n_start = n->start;
+            p_ofs = 0;
+        }
+        n_last = MIN(last, n->last);
+        p_len = (n_last + 1 - n_start) >> TARGET_PAGE_BITS;
+
+        t = container_of(n, TargetPageDataNode, itree);
+        memset(t->data[p_ofs], 0, p_len * TARGET_PAGE_DATA_SIZE);
     }
-#endif
 }
 
-#ifdef TARGET_PAGE_DATA_SIZE
 void *page_get_target_data(target_ulong address)
 {
-    PageDesc *p = page_find(address >> TARGET_PAGE_BITS);
-    void *ret = p->target_data;
+    IntervalTreeNode *n;
+    TargetPageDataNode *t;
+    target_ulong page, region;
 
-    if (!ret) {
-        ret = g_malloc0(TARGET_PAGE_DATA_SIZE);
-        p->target_data = ret;
+    page = address & TARGET_PAGE_MASK;
+    region = address & TBD_MASK;
+
+    n = interval_tree_iter_first(&targetdata_root, page, page);
+    if (!n) {
+        /*
+         * See util/interval-tree.c re lockless lookups: no false positives
+         * but there are false negatives.  If we find nothing, retry with
+         * the mmap lock acquired.  We also need the lock for the
+         * allocation + insert.
+         */
+        mmap_lock();
+        n = interval_tree_iter_first(&targetdata_root, page, page);
+        if (!n) {
+            t = g_new0(TargetPageDataNode, 1);
+            n = &t->itree;
+            n->start = region;
+            n->last = region | ~TBD_MASK;
+            interval_tree_insert(n, &targetdata_root);
+        }
+        mmap_unlock();
     }
-    return ret;
+
+    t = container_of(n, TargetPageDataNode, itree);
+    return t->data[(page - region) >> TARGET_PAGE_BITS];
 }
-#endif
+#else
+void page_reset_target_data(target_ulong start, target_ulong end) { }
+#endif /* TARGET_PAGE_DATA_SIZE */
 
 /* The softmmu versions of these helpers are in cputlb.c.  */