bsd-user: Catch up to run-time reserved_va math

Catch up to linux-user's 8f67b9c694d0, 13c13397556a, 2f7828b57293, and
95059f9c313a by Richard Henderson which made reserved_va a run-time
calculation, defaulting to nothing except in the case of 64-bit host
32-bit target. Also include the adjustment of the comment heading that
work submitted in the same patch stream. Since this is a direct copy,
squash it into one patch rather than follow the Linux evolution since
breaking this down further at this point doesn't make sense for this
"new code".

Signed-off-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

bsd-user/main.c

@@ -77,25 +77,16 @@ bool have_guest_base;
 # if HOST_LONG_BITS > TARGET_VIRT_ADDR_SPACE_BITS
 #  if TARGET_VIRT_ADDR_SPACE_BITS == 32 && \
       (TARGET_LONG_BITS == 32 || defined(TARGET_ABI32))
-#   define MAX_RESERVED_VA  0xfffffffful
+#   define MAX_RESERVED_VA(CPU)  0xfffffffful
 #  else
-#   define MAX_RESERVED_VA  ((1ul << TARGET_VIRT_ADDR_SPACE_BITS) - 1)
+#   define MAX_RESERVED_VA(CPU)  ((1ul << TARGET_VIRT_ADDR_SPACE_BITS) - 1)
 #  endif
 # else
-#  define MAX_RESERVED_VA  0
+#  define MAX_RESERVED_VA(CPU)  0
 # endif
 #endif
 
-/*
- * That said, reserving *too* much vm space via mmap can run into problems
- * with rlimits, oom due to page table creation, etc.  We will still try it,
- * if directed by the command-line option, but not by default.
- */
-#if HOST_LONG_BITS == 64 && TARGET_VIRT_ADDR_SPACE_BITS <= 32
-unsigned long reserved_va = MAX_RESERVED_VA;
-#else
 unsigned long reserved_va;
-#endif
 
 const char *interp_prefix = CONFIG_QEMU_INTERP_PREFIX;
 const char *qemu_uname_release;
@@ -293,6 +284,7 @@ int main(int argc, char **argv)
     envlist_t *envlist = NULL;
     char *argv0 = NULL;
     int host_page_size;
+    unsigned long max_reserved_va;
 
     adjust_ssize();
 
@@ -493,6 +485,29 @@ int main(int argc, char **argv)
     cpu_reset(cpu);
     thread_cpu = cpu;
 
+    /*
+     * Reserving too much vm space via mmap can run into problems with rlimits,
+     * oom due to page table creation, etc.  We will still try it, if directed
+     * by the command-line option, but not by default. Unless we're running a
+     * target address space of 32 or fewer bits on a host with 64 bits.
+     */
+    max_reserved_va = MAX_RESERVED_VA(cpu);
+    if (reserved_va != 0) {
+        if ((reserved_va + 1) % host_page_size) {
+            char *s = size_to_str(host_page_size);
+            fprintf(stderr, "Reserved virtual address not aligned mod %s\n", s);
+            g_free(s);
+            exit(EXIT_FAILURE);
+        }
+        if (max_reserved_va && reserved_va > max_reserved_va) {
+            fprintf(stderr, "Reserved virtual address too big\n");
+            exit(EXIT_FAILURE);
+        }
+    } else if (HOST_LONG_BITS == 64 && TARGET_VIRT_ADDR_SPACE_BITS <= 32) {
+        /* MAX_RESERVED_VA + 1 is a large power of 2, so is aligned. */
+        reserved_va = max_reserved_va;
+    }
+
     if (getenv("QEMU_STRACE")) {
         do_strace = 1;
     }