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

Christoffer Dall
2017-11-02T08:12:24Z

On Wed, Nov 01, 2017 at 03:23:50PM +0000, James Morse wrote:
> Hi guys,
>
> On 31/10/17 10:08, Will Deacon wrote:
> > On Tue, Oct 31, 2017 at 07:35:35AM +0100, Christoffer Dall wrote:
> >> On Thu, Oct 19, 2017 at 03:57:46PM +0100, James Morse wrote:
> >>> 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's 'what about mixed RAS support' comment will take me a while to get to
> fix, and I don't think I can test that before the end of the week.
>
> Unless there is an rc8+linux-next I think this is too late, but I will split off
> and repost the SError_rework bits as that seems uncontentious...
>
>

It is indeed cutting it a bit close. We'll have the same challenge of
either going via arm64 or using a stable branch we merge into the KVM
side for the next merge window as well. I prefer the latter, since
there's going to be some conflicts with my optimization series which I
hope to get in for v4.16.

Thanks,
-Christoffer