Re: [Xen-devel] [PATCH v2 2/3] xen/x86: add dom0 memory sizing variants

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.12.18 at 09:06, <jgross@xxxxxxxx> wrote:
> Today the memory size of dom0 can be specified only in terms of bytes
> (either an absolute value or "host-mem - value"). When dom0 shouldn't
> be auto-ballooned this requires nearly always a manual adaption of the
> Xen boot parameters to reflect the actual host memory size.
> 
> Add more possibilities to specify memory sizes. Today we have:
> 
> dom0_mem= List of ( min:<size> | max:<size> | <size> )
> 
> with <size> being a positive or negative size value (e.g. 1G).
> 
> Modify that to:
> 
> dom0_mem= List of ( min:<sz> | max:<sz> | <sz> )
> <sz>: <size> | [<size>+]<frac>%
> <frac>: integer value < 100
> 
> With the following semantics:
> 
> <frac>% specifies a fraction of host memory size in percent.
> <sz> is a percentage of host memory plus an offset.
> 
> So <sz> being 1G+25% on a 256G host would result in 65G.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

I notice though that ...

> -static long __init parse_amt(const char *s, const char **ps)
> +static int __init parse_amt(const char *s, const char **ps, struct memsize 
> *sz)
>  {
> -    long pages = parse_size_and_unit((*s == '-') ? s+1 : s, ps) >> 
> PAGE_SHIFT;
> -    return (*s == '-') ? -pages : pages;
> +    unsigned long val;
> +    struct memsize tmp = { };
> +
> +    tmp.minus = (*s == '-');
> +    if ( tmp.minus )
> +        s++;
> +
> +    /* Avoid accessing s[-1] in case value starts with '%'. */
> +    if ( *s == '%' )
> +        return -EINVAL;
> +
> +    while ( isdigit(*s) )
> +    {
> +        val = parse_size_and_unit_or_int(s, ps, '%');
> +        s = *ps;
> +        if ( *s == '%' )
> +        {
> +            if ( !isdigit(s[-1]) || val >= 100 )
> +                return -EINVAL;
> +            tmp.percent = val;
> +            s++;
> +        }
> +        else
> +            tmp.nr_pages = val >> PAGE_SHIFT;
> +        if ( *s == '+' )
> +            s++;
> +    }

... you allow more flexibility here than you document (i.e. also
<percentage>+<basesize>). You may want to consider
refusing something like 1G+10%+10%, though.

Jan



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