On Sat, Jun 01, 2024 at 10:47:47AM +0100, Marc Zyngier wrote: > On Sat, 01 Jun 2024 00:13:50 +0100, Oliver Upton <oliver.upton@xxxxxxxxx> wrote: > > +static bool kvm_hyp_handle_zcr(struct kvm_vcpu *vcpu, u64 *exit_code) > > +{ > > + u32 sysreg = esr_sys64_to_sysreg(kvm_vcpu_get_esr(vcpu)); > > + > > + if (!vcpu_has_nv(vcpu)) > > + return false; > > + > > + if (sysreg != SYS_ZCR_EL2) > > + return false; > > + > > + if (guest_owns_fp_regs()) > > + return false; > > + > > + return kvm_hyp_handle_fpsimd(vcpu, exit_code); > > For my own understanding of the flow: let's say the L1 guest accesses > ZCR_EL2 while the host own the FP regs: > > - ZCR_EL2 traps > - we restore the guest's state, enable SVE > - ZCR_EL2 traps again > - emulate the access on the slow path > > In contrast, the same thing using ZCR_EL1 in L1 results in: > > - ZCR_EL1 traps > - we restore the guest's state, enable SVE > > and we're done. > > Is that correct? If so, a comment would help... ;-) Yeah, and I agree having a comment for this would be a good idea. Now that I'm looking at this code again, I had wanted to avoid the second trap on ZCR_EL2, so I'll probably fold in a change to bounce out to the slow path after loading SVE state. -- Thanks, Oliver