Re: [Xen-devel] [PATCH v6 05/10] Clear AC bit in RFLAGS to protect Xen itself by SMAP

["Wu, Feng" <feng.wu@xxxxxxxxx>]

> -----Original Message-----
> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
> Sent: Wednesday, May 07, 2014 7:54 PM
> To: Jan Beulich
> Cc: Wu, Feng; ian.campbell@xxxxxxxxxx; Dong, Eddie; Nakajima, Jun; Tian,
> Kevin; xen-devel@xxxxxxxxxxxxx
> Subject: Re: [PATCH v6 05/10] Clear AC bit in RFLAGS to protect Xen itself by
> SMAP
> 
> On 07/05/14 12:40, Jan Beulich wrote:
> >>>> On 07.05.14 at 11:44, <andrew.cooper3@xxxxxxxxxx> wrote:
> >> On 07/05/14 09:19, Feng Wu wrote:
> >>> @@ -673,6 +675,7 @@ ENTRY(nmi_crash)
> >>>          ud2
> >>>
> >>>  ENTRY(machine_check)
> >>> +        ASM_CLAC
> >> This is not needed.  the start of handle_ist_exception has a SAVE_ALL,
> >> which also covers the nmi entry point.
> >>
> >> On the subject of IST exceptions, perhaps the double fault explicitly
> >> wants a STAC to reduce the likelihood of taking a further fault while
> >> trying to dump state. ?
> > I agree. And perhaps along with do_double_fault(), fatal_trap()
> > should then also get a stac() added?
> >
> > Jan
> >
> 
> With doubt_fault: being sole caller of do_double_fault(), editing the
> entry point in entry.S to "ASM_STAC; SAVE_ALL 0" is sufficient to avoid
> stac() in do_doube_fault() itself.

I think it's better to add "ASM_STAC" just before " call  do_double_fault".
Do you think this is okay, Andrew? Thanks!

> 
> I would agree that fatal_trap() wants an stac() in it.
> 
> ~Andrew

Thanks,
Feng

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