> -----Original Message----- > From: Christoffer Dall [mailto:christoffer.dall@xxxxxxx] > Sent: Tuesday, July 17, 2018 2:44 PM > To: Bharat Bhushan <bharat.bhushan@xxxxxxx> > Cc: kvmarm@xxxxxxxxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; > kvm@xxxxxxxxxxxxxxx; Marc Zyngier <marc.zyngier@xxxxxxx>; Andre > Przywara <andre.przywara@xxxxxxx> > Subject: Re: [PATCH v4 10/10] KVM: arm/arm64: vgic: Update documentation > of the GIC devices wrt IIDR > > On Mon, Jul 16, 2018 at 03:59:42PM +0000, Bharat Bhushan wrote: > > Hi Christoffer, > > > > > -----Original Message----- > > > From: kvmarm-bounces@xxxxxxxxxxxxxxxxxxxxx [mailto:kvmarm- > > > bounces@xxxxxxxxxxxxxxxxxxxxx] On Behalf Of Christoffer Dall > > > Sent: Monday, July 16, 2018 6:36 PM > > > To: kvmarm@xxxxxxxxxxxxxxxxxxxxx; > > > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > > > Cc: kvm@xxxxxxxxxxxxxxx; Marc Zyngier <marc.zyngier@xxxxxxx>; > Andre > > > Przywara <andre.przywara@xxxxxxx> > > > Subject: [PATCH v4 10/10] KVM: arm/arm64: vgic: Update documentation > > > of the GIC devices wrt IIDR > > > > > > Update the documentation to reflect the ordering requirements of > > > restoring the GICD_IIDR register before any other registers and the > > > effects this has on restoring the interrupt groups for an emulated > > > GICv2 insttance. > > > > > > Also remove some outdated limitations in the documentation while > > > we're at it. > > > > > > Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxx> > > > --- > > > Documentation/virtual/kvm/devices/arm-vgic-v3.txt | 8 ++++++++ > > > Documentation/virtual/kvm/devices/arm-vgic.txt | 15 +++++++++------ > > > 2 files changed, 17 insertions(+), 6 deletions(-) > > > > > > diff --git a/Documentation/virtual/kvm/devices/arm-vgic-v3.txt > > > b/Documentation/virtual/kvm/devices/arm-vgic-v3.txt > > > index 2408ab7..eba20ae 100644 > > > --- a/Documentation/virtual/kvm/devices/arm-vgic-v3.txt > > > +++ b/Documentation/virtual/kvm/devices/arm-vgic-v3.txt > > > @@ -100,6 +100,14 @@ Groups: > > > Note that distributor fields are not banked, but return the same value > > > regardless of the mpidr used to access the register. > > > > > > + GICD_IIDR.Revision is updated when the KVM implementation is > > > + changed > > > in a > > > + way directly observable by the guest or userspace. Userspace > > > + should > > > read > > > + GICD_IIDR from KVM and write back the read value to confirm its > > > expected > > > + behavior is aligned with the KVM implementation. Userspace should > set > > > + GICD_IIDR before setting any other registers. to ensure the expected > > > + behavior. > > > + > > > + > > > The GICD_STATUSR and GICR_STATUSR registers are architecturally > > > defined such > > > that a write of a clear bit has no effect, whereas a write with a set bit > > > clears that value. To allow userspace to freely set the values > > > of these two diff --git > > > a/Documentation/virtual/kvm/devices/arm-vgic.txt > > > b/Documentation/virtual/kvm/devices/arm-vgic.txt > > > index b3ce126..4ff7635 100644 > > > --- a/Documentation/virtual/kvm/devices/arm-vgic.txt > > > +++ b/Documentation/virtual/kvm/devices/arm-vgic.txt > > > @@ -49,9 +49,15 @@ Groups: > > > index is specified with the vcpu_index field. Note that most distributor > > > fields are not banked, but return the same value regardless of the > > > vcpu_index used to access the register. > > > - Limitations: > > > - - Priorities are not implemented, and registers are RAZ/WI > > > - - Currently only implemented for KVM_DEV_TYPE_ARM_VGIC_V2. > > > + > > > + GICD_IIDR.Revision is updated when the KVM implementation of an > > > emulated > > > + GICv2 is changed in a way directly observable by the guest or > userspace. > > > + Userspace should read GICD_IIDR from KVM and write back the > > > + read > > > value to > > > + confirm its expected behavior is aligned with the KVM > implementation. > > > + Userspace should set GICD_IIDR before setting any other registers > (both > > > + KVM_DEV_ARM_VGIC_GRP_DIST_REGS and > > > KVM_DEV_ARM_VGIC_GRP_CPU_REGS) to ensure > > > + the expected behavior. Unless GICD_IIDR has been set from > > > + userspace, > > > writes > > > + to the interrupt group registers (GICD_IGROUPR) are ignored. > > > > Newer user-space will write to GICD_IIDR, that mean interrupt-groups are > supported otherwise not. > > It only means that userspace can write interrupt groups, interrupt groups will > always be supported (and writable) from the guest's point of view with > newer kernels. > > An updated userspace (which writes IIDR) must know to either raise an error > if it sees a migration stream from an older QEMU or translate the interrupt > groups from 1 to 0 before writing them. > > > And when interrupt-groups are not supported then writes to > > GICD_IGROUPR are ignored (backward compatibility) > > Legacy userspace which doesn't write IIDR will not have the above logic so to > preserve migration support between an old kernel and a new kernel, both > with legacy userspace, we ignore userspace writes to the IGROUPRs in the > KVM interface for userspace which hasn't written IIDR. Thanks Christoffer, > > Hope this helps, > -Christoffer
