Re: [PATCH] target/arm: Honor HCR_EL2.TID3 trapping requirements

[Marc Zyngier]

On 2019-11-25 10:40, Will Deacon wrote:
> On Sat, Nov 23, 2019 at 11:56:18AM +0000, Marc Zyngier wrote:
> > HCR_EL2.TID3 mandates that access from EL1 to a long list of id
> > registers traps to EL2, and QEMU has so far ignored this 
> > requirement.
> >
> > This breaks (among other things) KVM guests that have PtrAuth 
> > enabled,
> > while the hypervisor doesn't want to expose the feature to its 
> > guest.
> > To achieve this, KVM traps the ID registers (ID_AA64ISAR1_EL1 in 
> > this
> > case), and masks out the unsupported feature.
> >
> > QEMU not honoring the trap request means that the guest observes
> > that the feature is present in the HW, starts using it, and dies
> > a horrible death when KVM injects an UNDEF, because the feature
> > *really* isn't supported.
> >
> > Do the right thing by trapping to EL2 if HCR_EL2.TID3 is set.
> >
> > Reported-by: Will Deacon <address@hidden>
> > Signed-off-by: Marc Zyngier <address@hidden>
> > ---
> > There is a number of other trap bits missing (TID[0-2], for 
> > example),
> > but this at least gets a mainline Linux going with cpu=max.
> >
> >  target/arm/helper.c | 75 
> > +++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 75 insertions(+)
>
> I took your fixes/el2_traps branch for a spin and I no longer get an
> unexpected undefined instruction trap on first access to the ptrauth 
> key
> registers during context-switch:
>
> Tested-by: Will Deacon <address@hidden>

Thanks for that. I'll post the whole series later today, though the 
other
bits are less critical.

Thanks,

        M.
--
Jazz is not dead. It just smells funny...