tcg: Round the tb_size default from qemu_get_host_physmem

If qemu_get_host_physmem returns an odd number of pages,
then physmem / 8 will not be a multiple of the page size.

The following was observed on a gitlab runner:

ERROR qtest-arm/boot-serial-test - Bail out!
ERROR:../util/osdep.c:80:qemu_mprotect__osdep: \
  assertion failed: (!(size & ~qemu_real_host_page_mask))

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Luis Pires <luis.pires@eldorado.org.br>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

tcg/region.c

@@ -470,26 +470,6 @@ static size_t tcg_n_regions(size_t tb_size, unsigned max_cpus)
   (DEFAULT_CODE_GEN_BUFFER_SIZE_1 < MAX_CODE_GEN_BUFFER_SIZE \
    ? DEFAULT_CODE_GEN_BUFFER_SIZE_1 : MAX_CODE_GEN_BUFFER_SIZE)
 
-static size_t size_code_gen_buffer(size_t tb_size)
-{
-    /* Size the buffer.  */
-    if (tb_size == 0) {
-        size_t phys_mem = qemu_get_host_physmem();
-        if (phys_mem == 0) {
-            tb_size = DEFAULT_CODE_GEN_BUFFER_SIZE;
-        } else {
-            tb_size = MIN(DEFAULT_CODE_GEN_BUFFER_SIZE, phys_mem / 8);
-        }
-    }
-    if (tb_size < MIN_CODE_GEN_BUFFER_SIZE) {
-        tb_size = MIN_CODE_GEN_BUFFER_SIZE;
-    }
-    if (tb_size > MAX_CODE_GEN_BUFFER_SIZE) {
-        tb_size = MAX_CODE_GEN_BUFFER_SIZE;
-    }
-    return tb_size;
-}
-
 #ifdef __mips__
 /*
  * In order to use J and JAL within the code_gen_buffer, we require
@@ -841,13 +821,29 @@ static int alloc_code_gen_buffer(size_t size, int splitwx, Error **errp)
  */
 void tcg_region_init(size_t tb_size, int splitwx, unsigned max_cpus)
 {
-    size_t page_size;
+    const size_t page_size = qemu_real_host_page_size;
     size_t region_size;
     size_t i;
     int have_prot;
 
-    have_prot = alloc_code_gen_buffer(size_code_gen_buffer(tb_size),
-                                      splitwx, &error_fatal);
+    /* Size the buffer.  */
+    if (tb_size == 0) {
+        size_t phys_mem = qemu_get_host_physmem();
+        if (phys_mem == 0) {
+            tb_size = DEFAULT_CODE_GEN_BUFFER_SIZE;
+        } else {
+            tb_size = QEMU_ALIGN_DOWN(phys_mem / 8, page_size);
+            tb_size = MIN(DEFAULT_CODE_GEN_BUFFER_SIZE, tb_size);
+        }
+    }
+    if (tb_size < MIN_CODE_GEN_BUFFER_SIZE) {
+        tb_size = MIN_CODE_GEN_BUFFER_SIZE;
+    }
+    if (tb_size > MAX_CODE_GEN_BUFFER_SIZE) {
+        tb_size = MAX_CODE_GEN_BUFFER_SIZE;
+    }
+
+    have_prot = alloc_code_gen_buffer(tb_size, splitwx, &error_fatal);
     assert(have_prot >= 0);
 
     /* Request large pages for the buffer and the splitwx.  */
@@ -862,9 +858,8 @@ void tcg_region_init(size_t tb_size, int splitwx, unsigned max_cpus)
      * As a result of this we might end up with a few extra pages at the end of
      * the buffer; we will assign those to the last region.
      */
-    region.n = tcg_n_regions(region.total_size, max_cpus);
-    page_size = qemu_real_host_page_size;
-    region_size = region.total_size / region.n;
+    region.n = tcg_n_regions(tb_size, max_cpus);
+    region_size = tb_size / region.n;
     region_size = QEMU_ALIGN_DOWN(region_size, page_size);
 
     /* A region must have at least 2 pages; one code, one guard */