Re: [RFC 02/12] KVM: arm/arm64: Document KVM_VGIC_V3_ADDR_TYPE_REDIST_REGION

From: Auger Eric
Date: Mon Mar 19 2018 - 16:56:25 EST


Hi Marc,

On 19/03/18 15:15, Marc Zyngier wrote:
> On 19/03/18 09:20, Eric Auger 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@xxxxxxxxxx>
>> ---
>> 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
>> + - base field encodes bits [51:12] the guest physical base address
>> + 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.
>
> 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.
Agreed. I hesitated but saw addresses were generally described with
bits[51:12] in regs such as PROPBASER/PENDBASER and I did not really
need the spare bits.
>
>> + - pfns encodes the size of the region in 64kB pages.
>> + Only valid for KVM_DEV_TYPE_ARM_VGIC_V3.
>
> "pfns" a bit of an odd name, and is a bit unnatural. Why don't we
> instead encode the number of redistributors? You've already imposed that
> a redistributor has 2 64kB pages,
I copied the description in KVM_VGIC_V3_ADDR_TYPE_REDIST ;-) I knew that
for GICv4 the number of 64kB pages per redist is different so I thought
it was more generic. But I don't have a strong opinion.
so let's take advantage of this by
> saving yet another bit.
>
> You could dedicate a couple of these bits as a selector for the ITS
> version (v3, v4 or whatever comes after that, if ever...). Just make 0
> the only valid version for the time being.
OK

Thanks

Eric
>
>> Errors:
>> -E2BIG: Address outside of addressable IPA range
>> -EINVAL: Incorrectly aligned address
>>
>
> Thanks,
>
> M.
>