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, and 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.

The usual approach for device reset of having userspace write
the reset values of the registers to the kernel via the register
read/write APIs doesn't work for the ITS because it has some
internal state (caches) which is not exposed as registers,
and there is no register interface for "drop cached data without
writing it back to RAM". So we need a KVM API which mimics the
hardware's reset line, to provide the equivalent behaviour to
a "pull the power cord out of the back of the machine" reset.

Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Eric Auger <eric.auger@redhat.com>
Reported-by: wanghaibin <wanghaibin.wang@huawei.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
This commit is contained in:
Eric Auger 2017-10-26 17:23:10 +02:00 committed by Christoffer Dall
parent 36d6961c2b
commit ae204f80ca
1 changed files with 20 additions and 0 deletions

View File

@ -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 +161,19 @@ 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:
----------------
RESET returns the ITS to the same state that it was when first created and
initialized. When the RESET command returns, the following things are
guaranteed:
- The ITS is not enabled and quiescent
GITS_CTLR.Enabled = 0 .Quiescent=1
- There is no internally cached state
- No collection or device table are used
GITS_BASER<n>.Valid = 0
- GITS_CBASER = 0, GITS_CREADR = 0, GITS_CWRITER = 0
- The ABI version is unchanged and remains the one set when the ITS
device was first created.