Re: [PATCH 04/36] xen/arm: add parsing function for cache coloring configuration

[Julien Grall <julien@xxxxxxx>]

On 22/03/2022 09:17, Luca Miccio wrote:
> Hi Julien,
Hi Luca,

> > > - way_size: The size of a LLC way in bytes. This value is mainly used
> > >     to calculate the maximum available colors on the platform.
> > We should only add command line option when they are a strong use case.
> > In documentation, you wrote that someone may want to overwrite the way
> > size for "specific needs".
> >
> > Can you explain what would be those needs?
> > - dom0_colors: The coloring configuration for Dom0, which also acts as
> > >     default configuration for any DomU without an explicit configuration.
> > > - xen_colors: The coloring configuration for the Xen hypervisor itself.
> > >
> > > A cache coloring configuration consists of a selection of colors to be
> > > assigned to a VM or to the hypervisor. It is represented by a set of
> > > ranges. Add a common function that parses a string with a
> > > comma-separated set of hyphen-separated ranges like "0-7,15-16" and
> > > returns both: the number of chosen colors, and an array containing their
> > > ids.
> > > Currently we support platforms with up to 128 colors.
> > Is there any reason this value is hardcoded in Xen rather than part of
> > the Kconfig?
> Not really at the time when this patch was created. But as we notify in
> patch 32,
> there is an assert that fails if we use a certain amount of colors. Maybe
> we should
> find a better way to store the color information.
You could use a bitmap. Xen already provide facilities to use them in 
the public interface (see xenctl_bitmap) and convert the Xen internal 
bitmap (see DECLARE_BITMAP).
Cheers,

--
Julien Grall