github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-11-07 06:17:02 +01:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

Documentation: KVM: Add the VGICv5 IRS save/restore sequences

Browse Source 
Document the ordering requirements for saving and restoring the GICv5
IRS state.

The IST state is exposed through KVM_DEV_ARM_VGIC_GRP_IST and is
copied to or from userspace-provided buffers. Saving the ISTs
therefore does not update guest memory, so userspace does not need to
serialize guest memory after saving the IST state.

On restore, userspace must create the vCPUs, configure the IRS
address, restore the number of SPIs, and initialize the VGIC before
restoring IRS state. The IRS MMIO registers may be restored in any
order, but the final IRS_IDR* state and the IRS_IST_CFGR/IRS_IST_BASER
state that describes any LPI IST must be restored before
KVM_DEV_ARM_VGIC_GRP_IST.  KVM uses that state to validate the
userspace IST buffers and allocate any host LPI IST.

The IRS_*_STATUSR registers are observational state in KVM. Userspace
may save them for validation or debugging, but they are not required
as restore input and do not need to be replayed.

Signed-off-by: Sascha Bischoff <sascha.bischoff@arm.com>
Link: https://patch.msgid.link/20260904113404.4051341-40-sascha.bischoff@arm.com
Signed-off-by: Marc Zyngier <maz@kernel.org>
This commit is contained in:
Sascha Bischoff 2026-09-04 11:54:05 +00:00 committed by Marc Zyngier
parent a7f442da92
commit 53e9639e75
1 changed files with 49 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

49
Documentation/virt/kvm/devices/arm-vgic-v5.rst
View File

@ -262,3 +262,52 @@ Groups:
or tracking pending interrupts
-ETIMEDOUT An IRS save/VM operation timed out
=========== ============================================================
IRS Save Sequence:
------------------
The following operations are required when saving the virtual GICv5 IRS:
a) Save the ISTs by issuing KVM_GET_DEVICE_ATTR on KVM_DEV_ARM_VGIC_GRP_IST.
b) Save the IRS MMIO register state by issuing KVM_GET_DEVICE_ATTR on
KVM_DEV_ARM_VGIC_GRP_IRS_REGS.
These two steps may be performed in either order. Saving the ISTs writes all
IST state to userspace-provided buffers and does not update guest memory.
IRS Restore Sequence:
---------------------
The following ordering must be followed when restoring the virtual GICv5 and
IRS:
a) Create vCPUs.
b) Provide the IRS base address by issuing KVM_SET_DEVICE_ATTR on
KVM_DEV_ARM_VGIC_GRP_ADDR
c) Restore the number of SPIs by issuing KVM_SET_DEVICE_ATTR on
KVM_DEV_ARM_VGIC_GRP_NR_IRQS.
d) Initialise the GIC - this sets up the default state and creates the SPI
IST - by issuing KVM_SET_DEVICE_ATTR on KVM_DEV_ARM_VGIC_GRP_CTRL with
KVM_DEV_ARM_VGIC_CTRL_INIT
e) Restore the IRS MMIO register state by issuing KVM_SET_DEVICE_ATTR on
KVM_DEV_ARM_VGIC_GRP_IRS_REGS. The IRS registers may be restored in any
order, but any IRS_IDR* state and the IRS_IST_CFGR/IRS_IST_BASER state
describing an LPI IST must be restored before restoring the ISTs. KVM uses
the restored IRS_IST_CFGR and IRS_IST_BASER state to allocate the LPI IST
during the following step.
f) Restore the ISTs by issuing KVM_SET_DEVICE_ATTR on
KVM_DEV_ARM_VGIC_GRP_IST.
The number of SPIs must be restored before VGIC initialization because
initialization allocates the SPI state and fixes the SPI range exposed by the
IRS ID registers.
The IRS's MMIO registers must be restored prior to restoring the ISTs as these
are used to convey the number of LPIs the guest has configured to KVM.
The various ``*_STATUSR`` registers are observational state in the current KVM
implementation. Userspace may save them for validation or debugging purposes,
but they are not required as restore input and do not need to be replayed during
restore.
Then vCPUs can be started.