From: Denis Mukhin <dmukhin@ford.com> 

conring buffer doesn't need to be aligned to it's size; it just needs to be
contiguous. Use xmalloc_bytes() in console_init_preirq() for run-time
conring buffer allocation.

Warn user when the conring size is being changed behind the user's
back during the console initialization.

Also, limit the user-selectable conring buffer size to the maximum of 2GB
and minimum of _CONRING_SIZE.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Denis Mukhin <dmukhin@ford.com>
---
Changes since v4:
- new patch
---
 xen/drivers/char/console.c | 28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index 3ad86fd436e2..9394ab2a89eb 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -463,20 +463,34 @@ static void cf_check conring_dump_keyhandler(unsigned char key)
 void __init console_init_ring(void)
 {
     char *ring;
-    unsigned int start, size, chunk, order, memflags;
+    unsigned int start, size, chunk;
     unsigned long flags;
 
     if ( !opt_conring_size )
         return;
 
-    order = get_order_from_bytes(max(opt_conring_size, conring_size));
-    memflags = MEMF_bits(crashinfo_maxaddr_bits);
-    while ( (ring = alloc_xenheap_pages(order, memflags)) == NULL )
+    opt_conring_size = max(opt_conring_size, conring_size);
+    size = ROUNDDOWN(opt_conring_size, PAGE_SIZE);
+    if ( size != opt_conring_size )
     {
-        BUG_ON(order == 0);
-        order--;
+        opt_conring_size = size;
+        printk(XENLOG_WARNING "Rounding down console ring size to multiple of %lu KiB.\n",
+               PAGE_SIZE >> 10);
     }
-    opt_conring_size = PAGE_SIZE << order;
+    if ( opt_conring_size >= GB(2) )
+    {
+        opt_conring_size = GB(2);
+        printk(XENLOG_WARNING "Limiting user-configured console ring size.\n");
+    }
+    else if ( opt_conring_size < _CONRING_SIZE )
+    {
+        opt_conring_size = _CONRING_SIZE;
+        printk(XENLOG_WARNING "Using compile-time console ring size.\n");
+    }
+
+    /* Contiguous buffer; does not need to be naturally aligned. */
+    ring = xmalloc_bytes(opt_conring_size);
+    BUG_ON(ring == NULL);
 
     nrspin_lock_irqsave(&console_lock, flags);
 
-- 
2.52.0