linux-kernel - Re: [PATCH 06/10] xen/setup: Only set identity mapping in E820 regions when privileged.

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Date:	Tue, 21 Dec 2010 14:37:01 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	linux-kernel@...r.kernel.org, hpa@...or.com,
	Jan Beulich <JBeulich@...ell.com>,
	xen-devel@...ts.xensource.com,
	Konrad Rzeszutek Wilk <konrad@...nel.org>
Subject: Re: [PATCH 06/10] xen/setup: Only set identity mapping in E820 regions
 when privileged.

On 12/21/2010 01:37 PM, Konrad Rzeszutek Wilk wrote:
> We do not want to set the identity mapping on E820 reserved
> regions when running as PV. This is b/c the 0->ISA_END_ADDRESS region
> would be considered identity and we would try to read DMI information
> and fail (since the pfn_to_mfn(mfn)==pfn) under PV guests.
>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> ---
>  arch/x86/xen/setup.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> index 752c865..34fb906 100644
> --- a/arch/x86/xen/setup.c
> +++ b/arch/x86/xen/setup.c
> @@ -160,7 +160,7 @@ static unsigned long __init xen_set_identity(const struct e820map *e820)
>  		if (end < start)
>  			continue;
>  
> -		if (e820->map[i].type != E820_RAM) {
> +		if (xen_initial_domain() && e820->map[i].type != E820_RAM) {
>  			for (pfn = PFN_UP(start); pfn < PFN_DOWN(end); pfn++)
>  				set_phys_to_machine(pfn, pfn);
>  			identity += pfn - PFN_UP(start);

So you're relying on the fact that the ISA area is the only non-RAM e820
entry in domU?  I think it would be better to do a specific exclusion
for the ISA area rather than this.

    J
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