Re: "Iomem mapping not permitted" during windows crash dump under GPLPV

[Keir Fraser <keir.fraser@eu.citrix.com>]

It's not really an i/o page. All 1s means INVALID_MFN, which means the p2m
lookup failed. I suppose Windows may think it is a valid pfn (e.g., an
emulated device?) but that kind of mem can't be granted and never could be.

 -- Keir

On 30/01/2010 05:26, "James Harper" <james.harper@bendigoit.com.au> wrote:

> I've recently noticed that my windows crash dumps fail at around 40-50%
> under GPLPV. 'xm dmesg' shows the following:
> 
> (XEN) grant_table.c:350:d0 Iomem mapping not permitted ffffffffffffffff
> (domain 865)
> 
> At first I thought that the cause was just a bug in my grant ref code
> but it just occurred to me that this could be happening when Windows
> tries to write out the physical page I have mapped for some other xen
> function. grant_table.c:350 is around here:
> 
> if ( !iomem_access_permitted(rd, frame, frame) )
> {
>   gdprintk(XENLOG_WARNING,
>            "Iomem mapping not permitted %lx (domain %d)\n",
>            frame, rd->domain_id);
>   rc = GNTST_general_error;
>   goto undo_out;
> }
> 
> So is that likely to be the cause? I haven't yet checked the pfn that is
> failing against the pages I've mapped for various things but the number
> seems plausible. It used to work... is that check new under 3.4.1-ish?
> 
> And whats the solution? At this stage the only think I can think of is
> that it might be reasonable to ignore a small amount of failed writes
> during a crash dump... I haven't yet researched if there is a way to
> tell windows not to write out a given page of memory when doing a crash
> dump.
> 
> Thanks
> 
> James
> 
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