[PATCH 6/7] arm64: KVM: vgic-v3: Prevent the guest from messing with ICC_SRE_EL1

[Christoffer Dall]

On Mon, May 23, 2016 at 01:37:02PM +0100, Marc Zyngier wrote:
> Both our GIC emulations are "strict", in the sense that we either
> emulate a GICv2 or a GICv3, and not a GICv3 with GICv2 legacy
> support.
> 
> But when running on a GICv3 host, we still allow the guest to
> tinker with the ICC_SRE_EL1 register during its time slice:
> it can switch SRE off, observe that it is off, and yet on the
> next world switch, find the SRE bit to be set again. Not very
> nice.
> 
> An obvious solution is to always trap accesses to ICC_SRE_EL1
> (by clearing ICC_SRE_EL2.Enable), and to let the handler return
> the programmed value on a read, or ignore the write.
> 
> That way, the guest can always observe that our GICv3 is SRE==1
> only.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>

Reviewed-by: Christoffer Dall <christoffer.dall at linaro.org>