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Re: [Xen-devel] [PATCH] xen: point xen_start_info to a dummy struct for PV on HVM guests

On Wed, Oct 03, 2012 at 02:37:53PM +0100, Stefano Stabellini wrote:
> PV on HVM guests don't have a start_info page mapped by Xen, so
> xen_start_info is just NULL for them.
> That is problem because other parts of the code expect xen_start_info to
> point to something valid, for example xen_initial_domain() is defined as
> follow:
> #define xen_initial_domain()    (xen_domain() && \
>                  xen_start_info->flags & SIF_INITDOMAIN)

.. introduced by commit 4c071ee5268f7234c3d084b6093bebccc28cdcba
("arm: initial Xen support)

> Allocate a dummy start_info struct and point xen_start_info to it, as we
> do on ARM.
> This is not going to change things for PV guests because
> xen_start_info is set by arch/x86/xen/xen-head.S:startup_xen.
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>

Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index bf788d3..5f242cb 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -96,7 +96,8 @@ EXPORT_SYMBOL(machine_to_phys_mapping);
>  unsigned long  machine_to_phys_nr;
>  EXPORT_SYMBOL(machine_to_phys_nr);
> -struct start_info *xen_start_info;
> +static struct start_info _xen_start_info;

And lets change that to
'xen_dummy_start_info' to keep in sync with the other dummy one.

And also add a commnt:

 * Since 'xen_initial_domain' dereferences the xen_start_info we need
 * a dummy structure filled with zeros (for PVHVM guests which initialize
 * this late). For PV guests we do not have to worry about this as the first
 * few instructions (startup_xen) set it  properly.
> +struct start_info *xen_start_info = &_xen_start_info;
>  EXPORT_SYMBOL_GPL(xen_start_info);
>  struct shared_info xen_dummy_shared_info;

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