Re: [PATCH v15 3/6] KVM: arm64: Forward GCS exceptions to nested guests

[Mark Brown <broonie@kernel.org>]

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On Wed, Aug 20, 2025 at 11:15:25PM +0100, Marc Zyngier wrote:
> Mark Brown <broonie@kernel.org> wrote:

> > GCS can generate exceptions with an EC of 0x2D (GCS Data Check
> > Exception) when data validation checks fail.  When running a nested
> > guest which has access to GCS such exceptions can be directed from EL0
> > to EL2 and therefore need to be forwarded to the guest hypervisor, add
> > handling for this.

> Why is it so? A GCS exception from EL0 should be routed to EL1, no
> matter what (either this is an L1 guest with EL1 pretending to be EL2,
> or this is an L2 guest that has its own EL1).

> Can you describe the case where we need to reinject the exception?

I think I'd got myself confused while looking at the HCR_EL2.TGE case
thinking we enabled that in some case.  I can't now see what I was
looking at there, pretty sure I'm just mistaken - thanks for spotting
that, unless I work out what I was thinking I'll drop this.

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