Re: [Xen-devel] [RFC PATCH 27/31] cpufreq: hack: perf->states isn't a real guest handle on ARM

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 9 Nov 2017, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> 
> This patch is just a temp solution to highlight a problem which
> should be resolved in a proper way.
> 
> set_px_pminfo() is intended to be called from platform hypercall
> where "perf" argument was entirely filled in by hwdom.
> 
> But unlike x86 we don't get this info from hwdom on ARM,
> we get it from other sources (device tree + firmware). In order to
> retain function interface, we emulate receiving hypercall and
> pass argument which function expects to see. Although "perf->states"
> looks like a guest handle it is not a real handle and we can't use
> copy_from_guest() over it. As only scpi-cpufreq sets XEN_PX_DATA flag
> use it as an indicator to do memcpy.
> 
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> CC: Jan Beulich <jbeulich@xxxxxxxx>
> CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: Julien Grall <julien.grall@xxxxxxxxxx>

As a reference, this patch has been discussed here:

https://marc.info/?l=xen-devel&m=151250698607186



> ---
>  xen/drivers/cpufreq/cpufreq.c | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/xen/drivers/cpufreq/cpufreq.c b/xen/drivers/cpufreq/cpufreq.c
> index 64e1ae7..1022cd1 100644
> --- a/xen/drivers/cpufreq/cpufreq.c
> +++ b/xen/drivers/cpufreq/cpufreq.c
> @@ -558,11 +558,22 @@ int set_px_pminfo(uint32_t acpi_id, struct 
> xen_processor_performance *dom0_px_in
>              ret = -ENOMEM;
>              goto out;
>          }
> -        if ( copy_from_guest(pxpt->states, dom0_px_info->states,
> -                             dom0_px_info->state_count) )
> +
> +        if ( dom0_px_info->flags == XEN_PX_DATA )
>          {
> -            ret = -EFAULT;
> -            goto out;
> +            struct xen_processor_px *states = (dom0_px_info->states).p;
> +
> +            memcpy(pxpt->states, states,
> +                   dom0_px_info->state_count * sizeof(struct 
> xen_processor_px));
> +        }
> +        else
> +        {
> +            if ( copy_from_guest(pxpt->states, dom0_px_info->states,
> +                                 dom0_px_info->state_count) )
> +            {
> +                ret = -EFAULT;
> +                goto out;
> +            }
>          }
>          pxpt->state_count = dom0_px_info->state_count;
>  
> -- 
> 2.7.4
> 

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