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. I tiny bit of rationale here would have been nice. As I understand it, if we're presenting the guest with a fully coherent system, there should never be a need to invalidate anything, because the guest will always see the most recent value no matter how it sings and dances, right? > > We still have to trap S/W though, if only to prevent the guest from > doing something bad. > > Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx> > --- > 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... > + */ Is it strictly true that the guest is broken if it does any form of S/W ops? Does the guest actually know that it's running on a fully coherent system, or is the argument that no software, ever, should do S/W, even for reboot etc.? I think this should have slightly more info, or that part of the comment should just be dropped, to avoid misleading future readers who don't have the full picture. > + if (!cpus_have_const_cap(ARM64_HAS_STAGE2_FWB)) > + kvm_set_way_flush(vcpu); > + > return true; > } > > -- > 2.17.1 > Besides the usual nits on commentary: Reviewed-by: Christoffer Dall <christoffer.dall@xxxxxxx>
