linux-kernel - [PATCH 8/9] KVM: arm/arm64: Document KVM_DEV_ARM_ITS_CTRL

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Message-Id: <1506346478-1631-9-git-send-email-eric.auger@redhat.com>
Date:   Mon, 25 Sep 2017 15:34:37 +0200
From:   Eric Auger <eric.auger@...hat.com>
To:     eric.auger.pro@...il.com, eric.auger@...hat.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        marc.zyngier@....com, cdall@...aro.org, peter.maydell@...aro.org,
        andre.przywara@....com, wanghaibin.wang@...wei.com
Cc:     wu.wubin@...wei.com
Subject: [PATCH 8/9] KVM: arm/arm64: Document KVM_DEV_ARM_ITS_CTRL_RESET

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 freed.

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 documents a new attribute, KVM_DEV_ARM_ITS_CTRL_RESET in
the KVM_DEV_ARM_VGIC_GRP_CTRL group.

Upon this action, we can reset registers and especially those
pointing to tables previously allocated by the guest and free
the internal data structures storing the list of devices, collections
and lpis.

Signed-off-by: Eric Auger <eric.auger@...hat.com>
Reported-by: wanghaibin <wanghaibin.wang@...wei.com>

---

v1 -> v2:
- Describe architecturally-defined reset values
---
 Documentation/virtual/kvm/devices/arm-vgic-its.txt | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/Documentation/virtual/kvm/devices/arm-vgic-its.txt b/Documentation/virtual/kvm/devices/arm-vgic-its.txt
index eb06beb..047358c 100644
--- a/Documentation/virtual/kvm/devices/arm-vgic-its.txt
+++ b/Documentation/virtual/kvm/devices/arm-vgic-its.txt
@@ -33,6 +33,10 @@ 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.
+      See "ITS Reset State" section.
+
     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.
@@ -157,3 +161,15 @@ Then vcpus can be started.
  - pINTID is the physical LPI ID; if zero, it means the entry is not valid
    and other fields are not meaningful.
  - ICID is the collection ID
+
+ ITS Reset State:
+ ----------------
+
+- the ITS is not enabled and quiescent:
+  GITS_CTLR.Enabled = 0 .Quiescent=1
+- caches are empty
+- No collection or device table is provisionned
+  GITS_BASER<n>.Valid = 0
+- the command queue is not allocated:
+  GITS_CBASER = 0, GITS_CREADR = 0, GITS_CWRITER = 0
+- The ABI version corresponds to the one set before reset
-- 
2.5.5