Hi Marc,

On 2020/2/29 3:16, Marc Zyngier wrote:

Hi Zenghui,

On 2020-02-20 03:55, Zenghui Yu wrote:

quoted

Hi Marc,

On 2020/2/14 22:57, Marc Zyngier wrote:

quoted

In order to let a guest buy in the new, active-less SGIs, we
need to be able to switch between the two modes.

Handle this by stopping all guest activity, transfer the state
from one mode to the other, and resume the guest.

Signed-off-by: Marc Zyngier <maz@kernel.org>

[...]

quoted

diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
index 1bc09b523486..2c9fc13e2c59 100644
--- a/virt/kvm/arm/vgic/vgic-v3.c
+++ b/virt/kvm/arm/vgic/vgic-v3.c

@@ -540,6 +540,8 @@ int vgic_v3_map_resources(struct kvm *kvm)

          goto out;
      }
  +    if (kvm_vgic_global_state.has_gicv4_1)
+        vgic_v4_configure_vsgis(kvm);
      dist->ready = true;
    out:

Is there any reason to invoke vgic_v4_configure_vsgis() here?
This is called on the first VCPU run, through kvm_vgic_map_resources().
Shouldn't the vSGI configuration only driven by a GICD_CTLR.nASSGIreq
writing (from guest, or from userspace maybe)?

What I'm trying to catch here is the guest that has been restored with
nASSGIreq set. At the moment, we don't do anything on the userspace
side, because the vmm could decide to write that particular bit
multiple times, and switching between the two modes is expensive (not
to mention that all the vcpus may not have been created yet).

Moving it to the first run makes all these pitfalls go away (we have the
final nASSSGIreq value, and all the vcpus are accounted for).

So what will happen on restoration is (roughly):

  - for GICR_ISPENR0: We will restore the pending status of vSGIs into
    software pending_latch, just like what we've done for normal SGIs.
  - for GICD_CTLR.nASSGIreq: We will only record the written value.
    (Note to myself: No invocation of configure_vsgis() in uaccess_write
     callback, I previously mixed it up with the guest write callback.)
  - Finally, you choose the first vcpu run as the appropriate point to
    potentially flush the pending status to HW according to the final
    nASSGIreq value.

Does this make sense to you?

Yeah, it sounds like a good idea! And please ignore what I've replied to
patch #15, I obviously missed your intention at that time, sorry...

But can we move this hunk to some places more appropriate, for example,
put it together with the GICD_CTLR's uaccess_write change? It might make
things a bit clearer for other reviewers. :-)


Thanks,
Zenghui


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