Re: [PATCH v4 00/21] SError rework + RAS&IESB for firmware first support

Will Deacon
2017-10-31T10:07:00Z

On Tue, Oct 31, 2017 at 07:35:35AM +0100, Christoffer Dall wrote:
> Hi James, Catalin, and Will,
>
> On Thu, Oct 19, 2017 at 03:57:46PM +0100, James Morse wrote:
> > Hello,
> >
> > The aim of this series is to enable IESB and add ESB-instructions to let us
> > kick any pending RAS errors into firmware to be handled by firmware-first.
> >
> > Not all systems will have this firmware, so these RAS errors will become
> > pending SErrors. We should take these as quickly as possible and avoid
> > panic()ing for errors where we could have continued.
> >
> > This first part of this series reworks the DAIF masking so that SError is
> > unmasked unless we are handling a debug exception.
> >
> > The last part provides the same minimal handling for SError that interrupt
> > KVM. KVM is currently unable to handle SErrors during world-switch, unless
> > they occur during a magic single-instruction window, it hyp-panics. I suspect
> > this will be easier to fix once the VHE world-switch is further optimised.
> >
> > KVMs kvm_inject_vabt() needs updating for v8.2 as now we can specify an ESR,
> > and all-zeros has a RAS meaning.
> >
> > KVM's existing 'impdef SError to the guest' behaviour probably needs revisiting.
> > These are errors where we don't know what they mean, they may not be
> > synchronised by ESB. Today we blame the guest.
> > My half-baked suggestion would be to make a virtual SError pending, but then
> > exit to user-space to give Qemu the change to quit (for virtual machines that
> > don't generate SError), pend an SError with a new Qemu-specific ESR, or blindly
> > continue and take KVMs default all-zeros impdef ESR.
>
> The KVM side of this series is looking pretty good.
>
> What are the merge plans for this? I am fine if you will take this via
> the arm64 tree with our acks from the KVM side. Alternatively, I
> suppose you can apply all the arm64 patches and provide us with a stable
> branch for that?

I'll take a look this afternoon, but we haven't had a linux next release
since the 18th so I'm starting to get nervous about conflicts if I end up
pulling in new trees now.

Will