[PATCH v3 9/9] arm64: KVM: vgic: deal with GIC sub-page alignment

[Christoffer Dall]

On Tue, Jul 08, 2014 at 12:09:08PM +0100, Marc Zyngier wrote:
> The GIC CPU interface is always 4k aligned. If the host is using
> 64k pages, it is critical to place the guest's GICC interface at the
> same relative alignment as the host's GICV. Failure to do so results
> in an impossibility for the guest to deal with interrupts.
> 
> Add a KVM_DEV_ARM_VGIC_GRP_ADDR_OFFSET attribute for the VGIC, allowing
> userspace to retrieve the GICV offset in a page. It becomes then trivial
> to adjust the GICC base address for the guest.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
> ---
>  arch/arm/include/uapi/asm/kvm.h   | 1 +
>  arch/arm64/include/uapi/asm/kvm.h | 1 +
>  virt/kvm/arm/vgic.c               | 7 +++++++
>  3 files changed, 9 insertions(+)
> 
> diff --git a/arch/arm/include/uapi/asm/kvm.h b/arch/arm/include/uapi/asm/kvm.h
> index 8b51c1a..056b782 100644
> --- a/arch/arm/include/uapi/asm/kvm.h
> +++ b/arch/arm/include/uapi/asm/kvm.h
> @@ -174,6 +174,7 @@ struct kvm_arch_memory_slot {
>  #define   KVM_DEV_ARM_VGIC_OFFSET_SHIFT	0
>  #define   KVM_DEV_ARM_VGIC_OFFSET_MASK	(0xffffffffULL << KVM_DEV_ARM_VGIC_OFFSET_SHIFT)
>  #define KVM_DEV_ARM_VGIC_GRP_NR_IRQS	3
> +#define KVM_DEV_ARM_VGIC_GRP_ADDR_OFFSET 4
>  
>  /* KVM_IRQ_LINE irq field index values */
>  #define KVM_ARM_IRQ_TYPE_SHIFT		24
> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> index b5cd6ed..5513de4 100644
> --- a/arch/arm64/include/uapi/asm/kvm.h
> +++ b/arch/arm64/include/uapi/asm/kvm.h
> @@ -160,6 +160,7 @@ struct kvm_arch_memory_slot {
>  #define   KVM_DEV_ARM_VGIC_OFFSET_SHIFT	0
>  #define   KVM_DEV_ARM_VGIC_OFFSET_MASK	(0xffffffffULL << KVM_DEV_ARM_VGIC_OFFSET_SHIFT)
>  #define KVM_DEV_ARM_VGIC_GRP_NR_IRQS	3
> +#define KVM_DEV_ARM_VGIC_GRP_ADDR_OFFSET 4
>  
>  /* KVM_IRQ_LINE irq field index values */
>  #define KVM_ARM_IRQ_TYPE_SHIFT		24
> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> index aee10da..1e60981 100644
> --- a/virt/kvm/arm/vgic.c
> +++ b/virt/kvm/arm/vgic.c
> @@ -2271,6 +2271,12 @@ static int vgic_get_attr(struct kvm_device *dev, struct kvm_device_attr *attr)
>  		r = put_user(dev->kvm->arch.vgic.nr_irqs, uaddr);
>  		break;
>  	}
> +	case KVM_DEV_ARM_VGIC_GRP_ADDR_OFFSET: {
> +		u32 __user *uaddr = (u32 __user *)(long)attr->addr;
> +		u32 val = vgic->vcpu_base & ~PAGE_MASK;
> +		r = put_user(val, uaddr);
> +		break;
> +	}
>  
>  	}
>  
> @@ -2308,6 +2314,7 @@ static int vgic_has_attr(struct kvm_device *dev, struct kvm_device_attr *attr)
>  		offset = attr->attr & KVM_DEV_ARM_VGIC_OFFSET_MASK;
>  		return vgic_has_attr_regs(vgic_cpu_ranges, offset);
>  	case KVM_DEV_ARM_VGIC_GRP_NR_IRQS:
> +	case KVM_DEV_ARM_VGIC_GRP_ADDR_OFFSET:
>  		return 0;
>  	}
>  	return -ENXIO;
> -- 
> 2.0.0
> 

Also here, add documentation to the fancy ABI:
Documentation/virtual/kvm/devices/arm-vgic.txt

When rebased onto the recent patches this will never return anything
else than 0 right?  Otherwise KVM would have failed to initialize and
bailed out.  What is our solution for this problem again?

-Christoffer