Re: [Qemu-arm] [Qemu-devel] [PATCH 0/2] GICv2 & GICv3: RAZ/WI reserved addresses rather than aborting

[Andrew Jones]

On Tue, Jan 09, 2018 at 04:35:30PM +0000, Peter Maydell wrote:
> On 9 January 2018 at 16:29, Laszlo Ersek <address@hidden> wrote:
> > On 01/09/18 17:12, Peter Maydell wrote:
> >> On 9 January 2018 at 15:58, Laszlo Ersek <address@hidden> wrote:
> >>> Sorry, no clue about any of this -- where should I read up?
> >>
> >> I cc'd you mostly as a heads-up since the QEMU bug is UEFI affecting,
> >> not because I wanted to make you read the GIC specs :-)
> >
> > Thanks (and, thanks :) ) -- from patch #2, looks like GICv2 is affected
> > too, and the patch seems to be fixing commit a9d853533cc1
> > ("hw/intc/arm_gic: Switch to read/write callbacks with tx attributes",
> > 2015-05-12).
> >
> > Is that right? That commit was released with v2.4.0. Should I have
> > experienced the error? Is it KVM / hardware specific? What are the symptoms?
> 
> Happens under TCG emulation only. The bug got introduced with
> commit c79c0a314c43b78f6, which changed the effect of a device
> returning MEMTX_ERROR/MEMTX_DECODE_ERROR from "RAZ/WI" to
> "guest data abort". That's in general the right thing to do,
> but in the case of these device models we were returning those
> values for cases which aren't supposed to provoke aborts.
> 
> The symptom is that if your guest code is poorly behaved and
> tries to read or write offsets that don't correspond to documented
> GIC registers, it will take an abort that it didn't before.
> Linux is fine; this UEFI image I have lying around stopped working.

Thanks for pointing this out. I had just recently noticed that the
'gicv3-active' kvm-unit-tests test had stopped passing on TCG, getting
DABTs when attempting to write GICD_ICACTIVER. I was just about to
complain in this thread that that register is indeed documented, but
now I see the implementation of the test was always wrong. It was using
the wrong register base, RD vs. SGI...

drew