Re: [Xen-devel] [PATCH 13/13] xen: allow more than 512 GB of RAM for 64 bit pv-domains

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 18/02/15 06:52, Juergen Gross wrote:
> 
> +if X86_64
> +choice
> +     prompt "Support pv-domains larger than 512GB"
> +     default XEN_512GB_NONE
> +     help
> +       Support paravirtualized domains with more than 512GB of RAM.
> +
> +       The Xen tools and crash dump analysis tools might not support
> +       pv-domains with more than 512 GB of RAM. This option controls the
> +       default setting of the kernel to use only up to 512 GB or more.
> +       It is always possible to change the default via specifying the
> +       boot parameter "xen_512gb_limit".
> +
> +     config XEN_512GB_NONE
> +             bool "neither dom0 nor domUs can be larger than 512GB"
> +     config XEN_512GB_DOM0
> +             bool "dom0 can be larger than 512GB, domUs not"
> +     config XEN_512GB_DOMU
> +             bool "domUs can be larger than 512GB, dom0 not"
> +     config XEN_512GB_ALL
> +             bool "dom0 and domUs can be larger than 512GB"
> +endchoice
> +endif

This configuration option doesn't look useful to me.  Can we get rid of
it with runtime checking.  e.g.,

If dom0, enable >512G.
If domU, enable >512G if requested by command line option /or/ toolstack
indicates that it supports the linear p2m.

And

If max_pfn < 512G, populate 3-level p2m /unless/ toolstack indicates it
supports the linear p2m.

People using crash analysis tools that need the 3-level p2m can clamp
dom0 memory with the Xen command line option.  FWIW, the tool we use
doesn't need this.

David


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