Re: [Xen-devel] PTE Write access is not set

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2011-12-14 at 09:41 +0000, Keir Fraser wrote:
> On 14/12/2011 09:36, "Ian Campbell" <Ian.Campbell@xxxxxxxxxx> wrote:
> 
> > On Wed, 2011-12-14 at 08:05 +0000, Liwei wrote:
> >> Hello list,
> >>     Using the 3.1.5 kernel and 4.1.3-rc1-pre xen (Latest ChangeSet:
> >> Tue Dec 06 10:53:12 2011 +0000 23199:d9f8316a8291), these crashes
> >> occur after about a day or so of running a HVM:
> >> =================8<=================
> >> (XEN) realmode.c:115:d9 Failed to emulate insn.
> >> (XEN) realmode.c:165:d9 Real-mode emulation failed @ e40a:00005f6c: d9
> >> 33 01 fc 30 34
> > 
> > I think this is FNSTENV/FSTENV which doesn't seem to be emulated by
> > Xen :-( xen/arch/x86/x86_emulate/x86_emulate.c has:
> >                  /* case 6: fstenv - TODO */
> 
> I wonder why a long-running HVM guest would be in real mode executing FP
> code. That seems a bit fishy.

I assumed it was some driver calling into a BIOS ROM or something
horrific like that. 

RFLAGS was 0x0000000000010002 (RF and the MB1 bit), no VM86 etc in
there.

CS is e40a -- Is that ring 2? surely not... I don't see anything in
Linux which uses that segment (it's not an easy grep though).

So, yes, fishy.

Ian.

> 
>  -- Keir
> 
> 



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