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

[Jan Beulich <jbeulich@xxxxxxxx>]

On 05.02.2026 02:36, dmukhin@xxxxxxx 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;
> +    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);

I'm sorry, but I'm going to veto any new uses of xmalloc_bytes(). As per the
comment at the top of xvmalloc.h, the family of functions there should be used
in new code. That family deliberately doesn't include a counterpart of
xmalloc_bytes(). You're wanting a multiple of page size anyway, so perhaps it
is warranted here to actually use vmalloc() directly.

Jan