Re: [PATCH 18/21] xenpaging: prevent page-out of first 16MB

[Olaf Hering <olaf@aepfle.de>]

On Fri, Dec 17, Jan Beulich wrote:

> >>> On 16.12.10 at 17:59, Olaf Hering <olaf@aepfle.de> wrote:
> > On Fri, Nov 26, Olaf Hering wrote:
> > 
> >> This is more a workaround than a bugfix:
> >> Don't page out first 16MB of memory.
> >> When the BIOS does its initialization process and xenpaging removes pages,
> >> crashes will occour due to lack of support of xenpaging.
> > 
> > While looking at this again, I came up with this change. Any idea whats
> > at 512K during BIOS startup?
> > 
> > 
> >  Subject: xenpaging: prevent page-out of gfn 0x80
> > 
> > Add a workaround for missing handling of paged-out pages during BIOS 
> > startup.
> > For some reason, only gfn 0x80 is affected.
> > 
> > (XEN) HVM3: HVM Loader
> > (XEN) traps.c:649:d3 Bad GMFN 80 (MFN ffffffffff) to MSR 40000000
> 
> This clearly is another place where page-in needs to be triggered.

Yes, thats true.
I had a printk in gfn_to_mfn for some months, and it did not trigger
during my testing. But then, I also had the patch which keeps the first
16MB in memory.

So as it stands, gfn_to_mfn() should call p2m_mem_paging_populate() at
least, even if that does not fix this crash.
I think the few gfn_to_mfn* variants should not return the paging types
anymore, and just sleep until the page is back. Thats something for next
year, as time runs out for me.

And: I think the various redefines of those functions/macros can go as well.


Olaf