Re: [Xen-devel] identify a Xen PV domU to fix devmem_is_allowed

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Feb 29, 2016 at 11:28:49AM +0100, Olaf Hering wrote:
> What is the correct way to identify a Xen PV domU in the kenrel?
> devmem_is_allowed() used to disable access to pages < 256 in domU.
> With pvops this check was removed, or never ported forward.

CC-ing Boris and Daniel.

Why is this needed? The first 640KB of memory in a guest are
RAM pages with no BIOS data in it.

> 
> Would this change be the correct fix?

.. A fix for what issue?
> 
> +++ b/arch/x86/mm/init.c
> @@ -637,7 +637,7 @@ void __init init_mem_mapping(void)
>  int devmem_is_allowed(unsigned long pagenr)
>  {
>         if (pagenr < 256)
> -               return 1;
> +               return !xen_pv_domain();
>         if (iomem_is_exclusive(pagenr << PAGE_SHIFT))
>                 return 0;
>         if (!page_is_ram(pagenr))
> 
> Olaf
> 
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