Re: [PATCH 5/5] arm64: KVM: vgic-v2: Enable GICV access from HYP if access from guest is unsafe

Peter Maydell
2016-08-19T12:53:48Z

On 19 August 2016 at 13:38, Marc Zyngier <marc.zyngier@arm.com> wrote:
> So far, we've been disabling KVM on systems where the GICV region couldn't
> be safely given to a guest. Now that we're able to handle this access
> safely by emulating it in HYP, we can enable this feature when we detect
> an unsafe configuration.
>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
> virt/kvm/arm/vgic/vgic-v2.c | 69 +++++++++++++++++++++++++++------------------
> 1 file changed, 42 insertions(+), 27 deletions(-)
>
> diff --git a/virt/kvm/arm/vgic/vgic-v2.c b/virt/kvm/arm/vgic/vgic-v2.c
> index b8da901..d1dcfc76 100644
> --- a/virt/kvm/arm/vgic/vgic-v2.c
> +++ b/virt/kvm/arm/vgic/vgic-v2.c
> @@ -278,12 +278,14 @@ int vgic_v2_map_resources(struct kvm *kvm)
> goto out;
> }
>
> - ret = kvm_phys_addr_ioremap(kvm, dist->vgic_cpu_base,
> - kvm_vgic_global_state.vcpu_base,
> - KVM_VGIC_V2_CPU_SIZE, true);
> - if (ret) {
> - kvm_err("Unable to remap VGIC CPU to VCPU\n");
> - goto out;
> + if (!static_branch_unlikely(&vgic_v2_cpuif_trap)) {
> + ret = kvm_phys_addr_ioremap(kvm, dist->vgic_cpu_base,
> + kvm_vgic_global_state.vcpu_base,
> + KVM_VGIC_V2_CPU_SIZE, true);
> + if (ret) {
> + kvm_err("Unable to remap VGIC CPU to VCPU\n");
> + goto out;
> + }
> }
>
> dist->ready = true;
> @@ -312,45 +314,51 @@ int vgic_v2_probe(const struct gic_kvm_info *info)
> return -ENXIO;
> }
>
> - if (!PAGE_ALIGNED(info->vcpu.start)) {
> - kvm_err("GICV physical address 0x%llx not page aligned\n",
> - (unsigned long long)info->vcpu.start);
> - return -ENXIO;
> - }
> + if (!PAGE_ALIGNED(info->vcpu.start) ||
> + !PAGE_ALIGNED(resource_size(&info->vcpu))) {
> + kvm_info("GICV region size/alignement is unsafe, using trapping\n");

"alignment".

Is it worth specifically saying "performance will be worse", or do we
expect this to only happen on systems where the h/w can't permit direct
access (as opposed to those with bad dt info) ?

thanks
-- PMM