On 2020/3/20 4:38, Auger Eric wrote:

Hi Marc,
On 3/19/20 1:10 PM, Marc Zyngier wrote:

quoted

Hi Zenghui,

On 2020-03-18 06:34, Zenghui Yu wrote:

quoted

Hi Marc,

On 2020/3/5 4:33, Marc Zyngier wrote:

quoted

The GICv4.1 architecture gives the hypervisor the option to let
the guest choose whether it wants the good old SGIs with an
active state, or the new, HW-based ones that do not have one.

For this, plumb the configuration of SGIs into the GICv3 MMIO
handling, present the GICD_TYPER2.nASSGIcap to the guest,
and handle the GICD_CTLR.nASSGIreq setting.

In order to be able to deal with the restore of a guest, also
apply the GICD_CTLR.nASSGIreq setting at first run so that we
can move the restored SGIs to the HW if that's what the guest
had selected in a previous life.

I'm okay with the restore path.  But it seems that we still fail to
save the pending state of vSGI - software pending_latch of HW-based
vSGIs will not be updated (and always be false) because we directly
inject them through ITS, so vgic_v3_uaccess_read_pending() can't
tell the correct pending state to user-space (the correct one should
be latched in HW).

It would be good if we can sync the hardware state into pending_latch
at an appropriate time (just before save), but not sure if we can...

The problem is to find the "appropriate time". It would require to define
a point in the save sequence where we transition the state from HW to
SW. I'm not keen on adding more state than we already have.

may be we could use a dedicated device group/attr as we have for the ITS
save tables? the user space would choose.

It means that userspace will be aware of some form of GICv4.1 details
(e.g., get/set vSGI state at HW level) that KVM has implemented.
Is it something that userspace required to know? I'm open to this ;-)

Thanks

Eric

quoted

But what we can do is to just ask the HW to give us the right state
on userspace access, at all times. How about this:

diff --git a/virt/kvm/arm/vgic/vgic-mmio-v3.c

b/virt/kvm/arm/vgic/vgic-mmio-v3.c
index 48fd9fc229a2..281fe7216c59 100644

--- a/virt/kvm/arm/vgic/vgic-mmio-v3.c
+++ b/virt/kvm/arm/vgic/vgic-mmio-v3.c

@@ -305,8 +305,18 @@ static unsigned long

vgic_v3_uaccess_read_pending(struct kvm_vcpu *vcpu,
       */
      for (i = 0; i < len * 8; i++) {
          struct vgic_irq *irq = vgic_get_irq(vcpu->kvm, vcpu, intid + i);
+        bool state = irq->pending_latch;

-        if (irq->pending_latch)
+        if (irq->hw && vgic_irq_is_sgi(irq->intid)) {
+            int err;
+
+            err = irq_get_irqchip_state(irq->host_irq,
+                            IRQCHIP_STATE_PENDING,
+                            &state);
+            WARN_ON(err);
+        }
+
+        if (state)
              value |= (1U << i);

          vgic_put_irq(vcpu->kvm, irq);

Anyway this looks good to me and will do the right thing on a userspace
save.

quoted

I can add this to "KVM: arm64: GICv4.1: Add direct injection capability
to SGI registers".

Thanks,
Zenghui


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