Re: [Xen-devel] [PATCH 1/2] x86/xen: set regions above the end of RAM as 1:1

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 3 Jan 2014, David Vrabel wrote:
> From: David Vrabel <david.vrabel@xxxxxxxxxx>
> 
> PCI devices may have BARs located above the end of RAM so mark such
> frames as identity frames in the p2m (instead of the default of
> missing).
> 
> PFNs outside the p2m (above MAX_P2M_PFN) are also considered to be
> identity frames for the same reason.
> 
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>

Shouldn't this be the case only for dom0?


>  arch/x86/xen/p2m.c   |    2 +-
>  arch/x86/xen/setup.c |   10 ++++++++++
>  2 files changed, 11 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
> index 2ae8699..a905355 100644
> --- a/arch/x86/xen/p2m.c
> +++ b/arch/x86/xen/p2m.c
> @@ -481,7 +481,7 @@ unsigned long get_phys_to_machine(unsigned long pfn)
>       unsigned topidx, mididx, idx;
>  
>       if (unlikely(pfn >= MAX_P2M_PFN))
> -             return INVALID_P2M_ENTRY;
> +             return IDENTITY_FRAME(pfn);
>  
>       topidx = p2m_top_index(pfn);
>       mididx = p2m_mid_index(pfn);
> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> index 68c054f..6d7798f 100644
> --- a/arch/x86/xen/setup.c
> +++ b/arch/x86/xen/setup.c
> @@ -412,6 +412,16 @@ char * __init xen_memory_setup(void)
>               max_pfn = min(MAX_DOMAIN_PAGES, last_pfn);
>               mem_end = PFN_PHYS(max_pfn);
>       }
> +
> +     /*
> +      * Set the rest as identity mapped, in case PCI BARs are
> +      * located here.
> +      *
> +      * PFNs above MAX_P2M_PFN are considered identity mapped as
> +      * well.
> +      */
> +     set_phys_range_identity(max_pfn + 1, ~0ul);
> +

Wouldn't this increase the size of the P2M considerably?


>        * Clamp the amount of extra memory to a EXTRA_MEM_RATIO
>        * factor the base size.  On non-highmem systems, the base
> -- 
> 1.7.2.5
> 
> 
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