Revert "linux-user/arm: Take more care allocating commpage"

This reverts commit 4f5c67f8df7f26e559509c68c45e652709edd23f.

This exposes bugs in target_mmap et al with respect to overflow
with the final page of the guest address space.  To be fixed in
the next development cycle.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

linux-user/elfload.c

@@ -423,32 +423,12 @@ enum {
 
 static bool init_guest_commpage(void)
 {
-    ARMCPU *cpu = ARM_CPU(thread_cpu);
-    abi_ptr want = HI_COMMPAGE & TARGET_PAGE_MASK;
-    abi_ptr addr;
-
-    /*
-     * M-profile allocates maximum of 2GB address space, so can never
-     * allocate the commpage.  Skip it.
-     */
-    if (arm_feature(&cpu->env, ARM_FEATURE_M)) {
-        return true;
-    }
-
-    /*
-     * If reserved_va does not cover the commpage, we get an assert
-     * in page_set_flags.  Produce an intelligent error instead.
-     */
-    if (reserved_va != 0 && want + TARGET_PAGE_SIZE - 1 > reserved_va) {
-        error_report("Allocating guest commpage: -R 0x%" PRIx64 " too small",
-                     (uint64_t)reserved_va + 1);
-        exit(EXIT_FAILURE);
-    }
-
-    addr = target_mmap(want, TARGET_PAGE_SIZE, PROT_READ | PROT_WRITE,
-                       MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1, 0);
+    abi_ptr commpage = HI_COMMPAGE & -qemu_host_page_size;
+    void *want = g2h_untagged(commpage);
+    void *addr = mmap(want, qemu_host_page_size, PROT_READ | PROT_WRITE,
+                      MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1, 0);
 
-    if (addr == -1) {
+    if (addr == MAP_FAILED) {
         perror("Allocating guest commpage");
         exit(EXIT_FAILURE);
     }
@@ -457,12 +437,15 @@ static bool init_guest_commpage(void)
     }
 
     /* Set kernel helper versions; rest of page is 0.  */
-    put_user_u32(5, 0xffff0ffcu);
+    __put_user(5, (uint32_t *)g2h_untagged(0xffff0ffcu));
 
-    if (target_mprotect(addr, qemu_host_page_size, PROT_READ | PROT_EXEC)) {
+    if (mprotect(addr, qemu_host_page_size, PROT_READ)) {
         perror("Protecting guest commpage");
         exit(EXIT_FAILURE);
     }
+
+    page_set_flags(commpage, commpage | ~qemu_host_page_mask,
+                   PAGE_READ | PAGE_EXEC | PAGE_VALID);
     return true;
 }