On Mon, Apr 10, 2017 at 10:19:43AM +0100, Marc Zyngier wrote:
> When emulating a GICv2-on-GICv3, special care must be taken to only
> save/restore VMCR_EL2 when ICC_SRE_EL1.SRE is cleared. Otherwise,
> all Group-0 interrupts end-up being delivered as FIQ, which is
> probably not what the guest expects, as demonstrated here with
> an unhappy EFI:
>
> FIQ Exception at 0x000000013BD21CC4
>
> This means that we cannot perform the load/put trick when dealing
> with VMCR_EL2 (because the host has SRE set), and we have to deal
> with it in the world-switch.
>
> Fortunately, this is not the most common case (modern guests should
> be able to deal with GICv3 directly), and the performance is not worse
> than what it was before the VMCR optimization.
>
> Signed-off-by: Marc Zyngier <[email protected]>
> ---
> virt/kvm/arm/hyp/vgic-v3-sr.c | 8 ++++++--
> virt/kvm/arm/vgic/vgic.c | 26 ++++++++++++++++++++------
> 2 files changed, 26 insertions(+), 8 deletions(-)
>
> diff --git a/virt/kvm/arm/hyp/vgic-v3-sr.c b/virt/kvm/arm/hyp/vgic-v3-sr.c
> index 3d0b1ddb6929..91922c1eddc8 100644
> --- a/virt/kvm/arm/hyp/vgic-v3-sr.c
> +++ b/virt/kvm/arm/hyp/vgic-v3-sr.c
> @@ -128,8 +128,10 @@ void __hyp_text __vgic_v3_save_state(struct kvm_vcpu
> *vcpu)
> * Make sure stores to the GIC via the memory mapped interface
> * are now visible to the system register interface.
> */
> - if (!cpu_if->vgic_sre)
> + if (!cpu_if->vgic_sre) {
> dsb(st);
> + cpu_if->vgic_vmcr = read_gicreg(ICH_VMCR_EL2);
> + }
>
> if (used_lrs) {
> int i;
> @@ -205,11 +207,13 @@ void __hyp_text __vgic_v3_restore_state(struct kvm_vcpu
> *vcpu)
> * delivered as a FIQ to the guest, with potentially fatal
> * consequences. So we must make sure that ICC_SRE_EL1 has
> * been actually programmed with the value we want before
> - * starting to mess with the rest of the GIC.
> + * starting to mess with the rest of the GIC, and VMCR_EL2 in
> + * particular.
> */
> if (!cpu_if->vgic_sre) {
> write_gicreg(0, ICC_SRE_EL1);
> isb();
> + write_gicreg(cpu_if->vgic_vmcr, ICH_VMCR_EL2);
> }
>
> val = read_gicreg(ICH_VTR_EL2);
> diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> index 3d0979c30721..32205f2ba6ff 100644
> --- a/virt/kvm/arm/vgic/vgic.c
> +++ b/virt/kvm/arm/vgic/vgic.c
> @@ -667,10 +667,20 @@ void kvm_vgic_load(struct kvm_vcpu *vcpu)
> if (unlikely(!vgic_initialized(vcpu->kvm)))
> return;
>
> - if (kvm_vgic_global_state.type == VGIC_V2)
> + if (kvm_vgic_global_state.type == VGIC_V2) {
> vgic_v2_load(vcpu);
> - else
> - vgic_v3_load(vcpu);
> + } else {
> + struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3;
> +
> + /*
> + * If dealing with a GICv2 emulation on GICv3,
> + * VMCR_EL2.VFIQen is dependent on ICC_SRE_EL1.SRE,
> + * and we have to perform the VMCR_EL2 save/restore in
> + * the world switch.
> + */
> + if (likely(cpu_if->vgic_sre))
> + vgic_v3_load(vcpu);
I wonder if this conditional should really be inside vgic_v3_load
instead?
> + }
> }
>
> void kvm_vgic_put(struct kvm_vcpu *vcpu)
> @@ -678,10 +688,14 @@ void kvm_vgic_put(struct kvm_vcpu *vcpu)
> if (unlikely(!vgic_initialized(vcpu->kvm)))
> return;
>
> - if (kvm_vgic_global_state.type == VGIC_V2)
> + if (kvm_vgic_global_state.type == VGIC_V2) {
> vgic_v2_put(vcpu);
> - else
> - vgic_v3_put(vcpu);
> + } else {
> + struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3;
> +
> + if (likely(cpu_if->vgic_sre))
> + vgic_v3_put(vcpu);
And same here?
> + }
> }
>
> int kvm_vgic_vcpu_pending_irq(struct kvm_vcpu *vcpu)
> --
> 2.11.0
>
Otherwise looks good.
Thanks,
-Christoffer
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