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    SubjectRe: [PATCH v3 02/12] KVM: arm/arm64: Document KVM_VGIC_V3_ADDR_TYPE_REDIST_REGION
    On Tue, Apr 24, 2018 at 05:50:37PM +0100, Peter Maydell wrote:
    > On 24 April 2018 at 17:46, Christoffer Dall <christoffer.dall@arm.com> wrote:
    > > On Fri, Apr 13, 2018 at 10:20:48AM +0200, Eric Auger wrote:
    > >> --- a/Documentation/virtual/kvm/devices/arm-vgic-v3.txt
    > >> +++ b/Documentation/virtual/kvm/devices/arm-vgic-v3.txt
    > >> @@ -27,9 +27,32 @@ 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 .... 16 | 15 - 12 |11 - 0
    > >> + values: | count | base | flags | index
    > >> + - index encodes the unique redistributor region index
    > >
    > > I'm not entirely sure I understand the purpose of the index field.
    > > Isn't a redistributor region identified uniquely by its base address?
    >
    > You need a way to tell the difference beween:
    > (1) redistributors for CPUs 0..63 at 0x40000000, redistributors
    > for 64..127 at 0x80000000
    > (2) redistributors for CPUs 0..63 at 0x80000000, redistributors
    > for 64..127 at 0x40000000
    >
    > The index field tells you which order the redistributor
    > regions go in.

    ah, right. This could be implied by the order creating the regions
    though, but ok, in that case it's nicer for userspace to state it
    explicitly.

    Thanks,
    -Christoffer

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