Re: [Xen-devel] [PATCH 3/3] xen/arm: Survive unknown traps from guests

[Julien Grall <julien.grall@xxxxxxx>]

On 05/04/2017 08:14 PM, Stefano Stabellini wrote:
> On Thu, 4 May 2017, Julien Grall wrote:
> > Currently we crash Xen if we see an ESR_EL2.EC value we don't recognise.
> > As configurable disables/enables are added to the architecture
> > (controlled by RES1/RESO bits respectively), with associated synchronous
> > exceptions, it may be possible for a guest to trigger exceptions with
> > classes that we don't recognise.
> >
> > While we can't service these exceptions in a manner useful to the guest,
> > we can avoid bringing down the host. Per ARM DDI 0487A.k_iss10775, page
> > D7-1937, EC values within the range 0x00 - 0x2c are reserved for future
> > use with synchronous exceptions, and EC within the range 0x2d - 0x3f may
> > be used for either synchronous or asynchronous exceptions.
> >
> > The patch makes Xen handle any unknown EC by injecting an UNDEFINED
> > exception into the guest, with a corresponding (ratelimited) warning in
> > the log.
> >
> > This patch is based on Linux commit f050fe7a9164 "arm: KVM: Survive unknown
> > traps from the guest".
> >
> > Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> > Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
> > ---
> >  xen/arch/arm/traps.c | 7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> > index c8ce62ff96..c0203da097 100644
> > --- a/xen/arch/arm/traps.c
> > +++ b/xen/arch/arm/traps.c
> > @@ -2926,9 +2926,10 @@ asmlinkage void do_trap_guest_sync(struct cpu_user_regs 
> > *regs)
> >          break;
> >
> >      default:
> > -        printk("Guest Trap. HSR=0x%x EC=0x%x IL=%x Syndrome=0x%"PRIx32"\n",
> > -               hsr.bits, hsr.ec, hsr.len, hsr.iss);
> > -        do_unexpected_trap("Guest", regs);
> > +        gprintk(XENLOG_WARNING,
> > +                "Guest Trap. HSR=0x%x EC=0x%x IL=%x Syndrome=0x%"PRIx32"\n",
> > +                hsr.bits, hsr.ec, hsr.len, hsr.iss);
> > +        inject_undef_exception(regs, hsr);
> >      }
> >  }
> I see you addressed my previous comment in this patch :-)
I wanted to keep the actual behavior in the previous patch (e.g panicing 
on unknown traps). I will have to resend the series to address Andrew's 
comment, so I can mention it in the commit message.
Cheers,

--
Julien Grall

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