Re: [PATCH v5 5/6] xen/console: update conring memory allocation

[Jan Beulich <jbeulich@suse.com>]

On 05.02.2026 02:36, dmukhin@xen.org wrote:
> --- 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;

I've spotted this removal only while looking at patch 6: How does this
work? We require conring_size to be a power of 2, or else masking by
(conring_size - 1) isn't a valid thing to do. You even touch
CONRING_IDX_MASK() twice in this series, so you really should have
noticed.

> +    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);
>