accel/tcg: Preserve PAGE_ANON when changing page permissions

Using mprotect() to change PROT_* does not change the MAP_ANON
previously set with mmap().  Our linux-user version of MTE only
works with MAP_ANON pages, so losing PAGE_ANON caused MTE to
stop working.

Reported-by: Stephen Long <steplong@quicinc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 7 insertions, 2 deletions

diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
index f32df8b240..ba6ab09790 100644
--- a/accel/tcg/translate-all.c
+++ b/accel/tcg/translate-all.c
@@ -2714,6 +2714,8 @@ void page_set_flags(target_ulong start, target_ulong end, int flags)
        a missing call to h2g_valid.  */
     assert(end - 1 <= GUEST_ADDR_MAX);
     assert(start < end);
+    /* Only set PAGE_ANON with new mappings. */
+    assert(!(flags & PAGE_ANON) || (flags & PAGE_RESET));
     assert_memory_lock();
 
     start = start & TARGET_PAGE_MASK;
@@ -2737,11 +2739,14 @@ void page_set_flags(target_ulong start, target_ulong end, int flags)
             p->first_tb) {
             tb_invalidate_phys_page(addr, 0);
         }
-        if (reset_target_data && p->target_data) {
+        if (reset_target_data) {
             g_free(p->target_data);
             p->target_data = NULL;
+            p->flags = flags;
+        } else {
+            /* Using mprotect on a page does not change MAP_ANON. */
+            p->flags = (p->flags & PAGE_ANON) | flags;
         }
-        p->flags = flags;
     }
 }