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Re: [Xen-devel] [PATCH] xen/arm: Blacklist the memory mapped timer (armv7-timer-mem)

On Tue, 2015-01-13 at 20:07 +0000, Julien Grall wrote:
> Some platform (such as the VFP Base AEMv8 model) has a memory mapped
> timer. We don't want DOM0 use this timer rather than the generic ARM
> timer. So blacklist it for all platforms.

It seems that these registers contain things like the ability to stop
the counter or change its frequency. So we certainly don't want dom0
getting at those!

It's not clear to me if accesses to these registers are trapped
according to the controls available for the CP registers, or if we would
have to resort to trapping the entire MMIO page if we wanted to support
access to these registers (I don't think we would want to anyway).

> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> ---
>     This patch is candidate to backport for Xen 4.5 and Xen 4.4.
>     It may not apply correctly for Xen 4.4.
> ---
>  xen/arch/arm/domain_build.c | 1 +
>  1 file changed, 1 insertion(+)
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index bf8dc78..16ce248 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -1047,6 +1047,7 @@ static int handle_node(struct domain *d, struct 
> kernel_info *kinfo,
>          DT_MATCH_COMPATIBLE("arm,psci"),
>          DT_MATCH_PATH("/cpus"),
>          DT_MATCH_TYPE("memory"),
> +        DT_MATCH_COMPATIBLE("arm,armv7-timer-mem"),

This is a bit less obvious that the other things in this list. Could you
perhaps add a comment?

>          { /* sentinel */ },
>      };
>      static const struct dt_device_match gic_matches[] __initconst =

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