Use qemu_real_host_page_size.
If the commpage is not within reserved_va, use MAP_FIXED_NOREPLACE.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Acked-by: Helge Deller <deller@gmx.de>
Message-Id: <20240102015808.132373-8-richard.henderson@linaro.org>
---
 linux-user/elfload.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index a9f1077861..f3f1ab4f69 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -460,6 +460,7 @@ enum {
 static bool init_guest_commpage(void)
 {
     ARMCPU *cpu = ARM_CPU(thread_cpu);
+    int host_page_size = qemu_real_host_page_size();
     abi_ptr commpage;
     void *want;
     void *addr;
@@ -472,10 +473,12 @@ static bool init_guest_commpage(void)
         return true;
     }
 
-    commpage = HI_COMMPAGE & -qemu_host_page_size;
+    commpage = HI_COMMPAGE & -host_page_size;
     want = g2h_untagged(commpage);
-    addr = mmap(want, qemu_host_page_size, PROT_READ | PROT_WRITE,
-                MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1, 0);
+    addr = mmap(want, host_page_size, PROT_READ | PROT_WRITE,
+                MAP_ANONYMOUS | MAP_PRIVATE |
+                (commpage < reserved_va ? MAP_FIXED : MAP_FIXED_NOREPLACE),
+                -1, 0);
 
     if (addr == MAP_FAILED) {
         perror("Allocating guest commpage");
@@ -488,12 +491,12 @@ static bool init_guest_commpage(void)
     /* Set kernel helper versions; rest of page is 0.  */
     __put_user(5, (uint32_t *)g2h_untagged(0xffff0ffcu));
 
-    if (mprotect(addr, qemu_host_page_size, PROT_READ)) {
+    if (mprotect(addr, host_page_size, PROT_READ)) {
         perror("Protecting guest commpage");
         exit(EXIT_FAILURE);
     }
 
-    page_set_flags(commpage, commpage | ~qemu_host_page_mask,
+    page_set_flags(commpage, commpage | (host_page_size - 1),
                    PAGE_READ | PAGE_EXEC | PAGE_VALID);
     return true;
 }
-- 
2.34.1