[PATCH v2 2/6] arm64: KVM: Handle Set/Way CMOs as NOPs if FWB is present

Mark Rutland
2018-05-31T11:51:27Z

On Wed, May 30, 2018 at 01:47:02PM +0100, Marc Zyngier wrote:
> Set/Way handling is one of the ugliest corners of KVM. We shouldn't
> have to handle that, but better safe than sorry.
>
> Thankfully, FWB fixes this for us by not requiering any maintenance
> whatsoever, which means we don't have to emulate S/W CMOs, and don't
> have to track VM ops either.
>
> We still have to trap S/W though, if only to prevent the guest from
> doing something bad.

S/W ops *also* do I-cache maintenance, so we'd still need to emulate
that. Though it looks like we're missing that today...

>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
> arch/arm64/kvm/sys_regs.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 6e3b969391fd..9a740f159245 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -195,7 +195,13 @@ static bool access_dcsw(struct kvm_vcpu *vcpu,
> if (!p->is_write)
> return read_from_write_only(vcpu, p, r);
>
> - kvm_set_way_flush(vcpu);
> + /*
> + * Only track S/W ops if we don't have FWB. It still indicates
> + * that the guest is a bit broken...
> + */
> + if (!cpus_have_const_cap(ARM64_HAS_STAGE2_FWB))
> + kvm_set_way_flush(vcpu);
> +

Assuming we implement I-cache maintenance, we can have something like:

if (!cpus_have_const_cap(ARM64_HAS_STAGE2_FWB))
kvm_set_way_flush_dcache(vcpu);

kvm_set_way_flush_icache(vcpu);

Thanks,
Mark.

> return true;
> }
>
> --
> 2.17.1
>