Re: [PATCH v1 10/11] KVM: arm64: Add primitives to flush/sync the VGIC state at EL2

[Fuad Tabba]

On Thu, 18 Jun 2026 at 11:10, Marc Zyngier <maz@xxxxxxxxxx> wrote:
>
> On Fri, 12 Jun 2026 07:59:24 +0100,
> tabba@xxxxxxxxxx wrote:
> >
> > From: Marc Zyngier <maz@xxxxxxxxxx>
> >
> > pKVM performs its own world switch for protected VMs but has no
> > primitives to move the per-vCPU VGIC state between the host and
> > hypervisor vCPU contexts.
> >
> > Add flush_hyp_vgic_state() and sync_hyp_vgic_state(). Flush copies
> > vgic_hcr, the in-use list registers and used_lrs from the host into the
> > hyp vCPU and pins vgic_sre to a fixed value; sync copies vgic_hcr,
> > vgic_vmcr and the in-use list registers back. The active priority
> > registers are handled separately by the save/restore-aprs path.
> >
> > Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> > Co-developed-by: Fuad Tabba <tabba@xxxxxxxxxx>
> > Signed-off-by: Fuad Tabba <tabba@xxxxxxxxxx>
> > ---
> >  arch/arm64/kvm/hyp/nvhe/hyp-main.c | 50 +++++++++++++++++++++++++-----
> >  1 file changed, 42 insertions(+), 8 deletions(-)
> >
> > diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> > index 2f165b6c7b07..23e644c24a03 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> > @@ -99,6 +99,46 @@ static void fpsimd_sve_sync(struct kvm_vcpu *vcpu)
> >       *host_data_ptr(fp_owner) = FP_STATE_HOST_OWNED;
> >  }
> >
> > +static void flush_hyp_vgic_state(struct pkvm_hyp_vcpu *hyp_vcpu)
> > +{
> > +     struct kvm_vcpu *host_vcpu = hyp_vcpu->host_vcpu;
> > +     struct vgic_v3_cpu_if *host_cpu_if, *hyp_cpu_if;
> > +     unsigned int used_lrs, max_lrs, i;
> > +
> > +     host_cpu_if     = &host_vcpu->arch.vgic_cpu.vgic_v3;
> > +     hyp_cpu_if      = &hyp_vcpu->vcpu.arch.vgic_cpu.vgic_v3;
> > +
> > +     max_lrs         = (read_gicreg(ICH_VTR_EL2) & ICH_VTR_EL2_ListRegs) + 1;
>
> This really needs to be rebased on the current state of kvmarm/next,
> particularly 8cc8bbbfab14c ("KVM: arm64: Bound used_lrs when flushing
> the pKVM hyp vCPU").
>
> I really want to avoid using ICH_VTR_EL2 on each and every entry to
> the guest, as this has really bad performance impacts when running
> this under NV (which is the only way I run pKVM).

Will do.

Thanks,
/fuad

>
> Thanks,
>
>         M.
>
> --
> Without deviation from the norm, progress is not possible.