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SubjectRe: [RFC 02/12] KVM: arm/arm64: Document KVM_VGIC_V3_ADDR_TYPE_REDIST_REGION
On 19 March 2018 at 09:20, Eric Auger <eric.auger@redhat.com> wrote:
> We introduce a new KVM_VGIC_V3_ADDR_TYPE_REDIST_REGION attribute in
> KVM_DEV_ARM_VGIC_GRP_ADDR group. It allows userspace to provide the
> base address and size of a redistributor region
>
> Compared to KVM_VGIC_V3_ADDR_TYPE_REDIST, this new attribute allows
> to declare several separate redistributor regions.
>
> So the whole redist space does not need to be contiguous anymore.
>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> ---
> Documentation/virtual/kvm/devices/arm-vgic-v3.txt | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/Documentation/virtual/kvm/devices/arm-vgic-v3.txt b/Documentation/virtual/kvm/devices/arm-vgic-v3.txt
> index 9293b45..2c0bedf 100644
> --- a/Documentation/virtual/kvm/devices/arm-vgic-v3.txt
> +++ b/Documentation/virtual/kvm/devices/arm-vgic-v3.txt
> @@ -27,6 +27,18 @@ Groups:
> VCPU and all of the redistributor pages are contiguous.
> Only valid for KVM_DEV_TYPE_ARM_VGIC_V3.
> This address needs to be 64K aligned.
> +
> + KVM_VGIC_V3_ADDR_TYPE_REDIST_REGION (rw, 64-bit)
> + The attr field of kvm_device_attr encodes 3 values:
> + bits: | 63 .... 52 | 51 .... 12 |11 - 0
> + values: | pfns | base | index
> + - index encodes the unique redistibutor region index

"redistributor"

> + - base field encodes bits [51:12] the guest physical base address

"of the guest"

> + of the first redistributor in the region. There are two 64K pages
> + for each VCPU and all of the redistributor pages are contiguous
> + within the redistributor region.
> + - pfns encodes the size of the region in 64kB pages.
> + Only valid for KVM_DEV_TYPE_ARM_VGIC_V3.

You should say something here about what happens if userspace
tries to use both KVM_VGIC_V3_ADDR_TYPE_REDIST_REGION and
KVM_VGIC_V3_ADDR_TYPE_REDIST. I think this should be an error
(reported by whichever of the two you try to set second).

> Errors:
> -E2BIG: Address outside of addressable IPA range
> -EINVAL: Incorrectly aligned address

Marc wrote:
> Why does base have to include bits [15:12] of the IPA? If it is 64kB
> aligned (as it should), these bits are guaranteed to be 0. This also
> avoid having to return -EINVAL in case of alignment problems.

If you're not using the bits for anything else you want to
check they're 0 anyway. Otherwise we can't guarantee to safely
use them for something else in future, because userspace might
be handing us garbage in those bits without noticing.

thanks
-- PMM

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