Re: [PATCH] KVM: arm64: Check GICV address is placed at a 4Kb boundary

[Christoffer Dall <christoffer.dall@linaro.org>]

Hi Itaru,

On Wed, Jun 29, 2016 at 03:22:45PM +0900, Itaru Kitayama wrote:
> Make sure GICV physical address is placed at a 4Kb boundary as spec
> says, not host kernel's page boundary. This prevents !4Kb kernels
> from returning an ENXIO prematurely during the KVM init phase at
> boot.
> Tested on Overdrive 3000 with 64Kb page-size kernel with ACPI.
> 
> Signed-off-by: Itaru Kitayama <itaru.kitayama@riken.jp>
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> 
> 
> diff --git a/virt/kvm/arm/vgic/vgic-v2.c b/virt/kvm/arm/vgic/vgic-v2.c
> index e31405e..0123e5d 100644
> --- a/virt/kvm/arm/vgic/vgic-v2.c
> +++ b/virt/kvm/arm/vgic/vgic-v2.c
> @@ -309,17 +309,15 @@ 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",
> +       if (!IS_ALIGNED(info->vcpu.start, SZ_4K)) {
> +               kvm_err("GICV physical address 0x%llx not 4Kb aligned\n",
>                         (unsigned long long)info->vcpu.start);
>                 return -ENXIO;
>         }
> 
> -       if (!PAGE_ALIGNED(resource_size(&info->vcpu))) {
> -               kvm_err("GICV size 0x%llx not a multiple of page
> size 0x%lx\n",
> -                       (unsigned long long)resource_size(&info->vcpu),
> +       if (!PAGE_ALIGNED(resource_size(&info->vcpu)))
> +               kvm_warn("GICV size 0x%llx not a multiple of page
> size 0x%lx, system may be unsafe\n", (unsigned long
> long)resource_size(&info->vcpu),
>                         PAGE_SIZE);
> -               return -ENXIO;
>         }
> 
>         kvm_vgic_global_state.vctrl_base = ioremap(info->vctrl.start,

Doesn't this change carry the risk of KVM mapping a page (larger than
4K) containing other things than the GICV interface into the guest,
potentially breaking isolation of the VM from host hardware resources?

-Christoffer