Re: fix for "xen: use maximum reservation to limit amount of usable RAM" - patch titled: "xen/e820: if there is not dom0_mem, don't tweak extra_pages."

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Tue, Sep 13, 2011 at 11:01:50AM +0100, David Vrabel wrote:
> On 12/09/11 21:13, Konrad Rzeszutek Wilk wrote:
> > .breaks one of my boxes (Core i3-2100), with Xen 4.1.1 (with and w/out the
> > 23790 changset in it).
> > 
> > I've traced it down to the fact that I booted my dom0 without
> > dom0_mem=X flag with a machine that has more than 8GB. Weirdly enough
> > I can only reproduce this under Intel boxes.
> > 
> > Anyhow this patch fixes it for me.
> 
> I think this patch is simpler.  Does it fix the issue?

Yes. Let me use that instead.
> 
> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> index c3b8d44..46d6d21 100644
> --- a/arch/x86/xen/setup.c
> +++ b/arch/x86/xen/setup.c
> @@ -306,10 +306,12 @@ char * __init xen_memory_setup(void)
>  	sanitize_e820_map(e820.map, ARRAY_SIZE(e820.map), &e820.nr_map);
>  
>  	extra_limit = xen_get_max_pages();
> -	if (extra_limit >= max_pfn)
> -		extra_pages = extra_limit - max_pfn;
> -	else
> -		extra_pages = 0;
> +	if (max_pfn + extra_pages > extra_limit) {
> +		if (extra_limit > max_pfn)
> +			extra_pages = extra_limit - max_pfn;
> +		else
> +			extra_pages = 0;
> +	}
>  
>  	extra_pages += xen_return_unused_memory(xen_start_info->nr_pages, &e820);
>  
> David