[RFC] KVM: arm/arm64: Introduce KVM_DEV_ARM_ITS_CTRL_RESET

[Eric Auger]

At the moment, the in-kernel emulated ITS is not properly reset.
On guest restart/reset some registers keep their old values and
internal structures like device, ITE, collection lists are not emptied.

This may lead to various bugs. Among them, we can have incorrect state
backup or failure when saving the ITS state at early guest boot stage.

This patch introduces a new attribute, KVM_DEV_ARM_ITS_CTRL_RESET in
the KVM_DEV_ARM_VGIC_GRP_CTRL group.

Upon this action, we can invalidate the various memory structures
pointed by GITS_BASERn and GITS_CBASER, free the ITS internal caches
and reset the relevant registers.

Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>

---

An alternative would consist in having the userspace writing
individual registers with default values: GITS_BASERn, GITS_CBASER
and GITS_CTLR. On kernel side we would reset related lists when
detecting the valid bit is set to false.
---
 Documentation/virtual/kvm/devices/arm-vgic-its.txt | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Documentation/virtual/kvm/devices/arm-vgic-its.txt b/Documentation/virtual/kvm/devices/arm-vgic-its.txt
index eb06beb..ebb15c5 100644
--- a/Documentation/virtual/kvm/devices/arm-vgic-its.txt
+++ b/Documentation/virtual/kvm/devices/arm-vgic-its.txt
@@ -33,6 +33,9 @@ Groups:
       request the initialization of the ITS, no additional parameter in
       kvm_device_attr.addr.
 
+    KVM_DEV_ARM_ITS_CTRL_RESET
+      reset the ITS, no additional parameter in kvm_device_attr.addr.
+
     KVM_DEV_ARM_ITS_SAVE_TABLES
       save the ITS table data into guest RAM, at the location provisioned
       by the guest in corresponding registers/table entries.
-- 
2.5.5