Use qemu_real_host_page_size.
If !reserved_va, use MAP_FIXED_NOREPLACE.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 linux-user/elfload.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 939c9b4df1..025747a15c 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -1355,10 +1355,14 @@ static bool init_guest_commpage(void)
                  0x3a, 0x68, 0x3b, 0x00,  /* trap 0 */
     };
 
-    void *want = g2h_untagged(LO_COMMPAGE & -qemu_host_page_size);
-    void *addr = mmap(want, qemu_host_page_size, PROT_READ | PROT_WRITE,
-                      MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1, 0);
+    int host_page_size = qemu_real_host_page_size();
+    void *want, *addr;
 
+    want = g2h_untagged(LO_COMMPAGE & -host_page_size);
+    addr = mmap(want, host_page_size, PROT_READ | PROT_WRITE,
+                MAP_ANONYMOUS | MAP_PRIVATE |
+                (reserved_va ? MAP_FIXED : MAP_FIXED_NOREPLACE),
+                -1, 0);
     if (addr == MAP_FAILED) {
         perror("Allocating guest commpage");
         exit(EXIT_FAILURE);
@@ -1367,9 +1371,9 @@ static bool init_guest_commpage(void)
         return false;
     }
 
-    memcpy(addr, kuser_page, sizeof(kuser_page));
+    memcpy(g2h_untagged(LO_COMMPAGE), kuser_page, sizeof(kuser_page));
 
-    if (mprotect(addr, qemu_host_page_size, PROT_READ)) {
+    if (mprotect(addr, host_page_size, PROT_READ)) {
         perror("Protecting guest commpage");
         exit(EXIT_FAILURE);
     }
-- 
2.34.1