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[v3,11/11] KVM: arm64: Clarify the ordering requirements for vcpu/RD creation

Message ID 20230927090911.3355209-12-maz@kernel.org (mailing list archive)
State New, archived
Headers show
Series KVM: arm64: Accelerate lookup of vcpus by MPIDR values (and other fixes) | expand

Commit Message

Marc Zyngier Sept. 27, 2023, 9:09 a.m. UTC 
It goes without saying, but it is probably better to spell it out:

If userspace tries to restore and VM, but creates vcpus and/or RDs
in a different order, the vcpu/RD mapping will be different. Yes,
our API is an ugly piece of crap and I can't believe that we missed
this.

If we want to relax the above, we'll need to define a new userspace
API that allows the mapping to be specified, rather than relying
on the kernel to perform the mapping on its own.

Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 Documentation/virt/kvm/devices/arm-vgic-v3.rst | 7 +++++++
 1 file changed, 7 insertions(+)
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Patch

diff --git a/Documentation/virt/kvm/devices/arm-vgic-v3.rst b/Documentation/virt/kvm/devices/arm-vgic-v3.rst
index 51e5e5762571..5817edb4e046 100644
--- a/Documentation/virt/kvm/devices/arm-vgic-v3.rst
+++ b/Documentation/virt/kvm/devices/arm-vgic-v3.rst
@@ -59,6 +59,13 @@  Groups:
   It is invalid to mix calls with KVM_VGIC_V3_ADDR_TYPE_REDIST and
   KVM_VGIC_V3_ADDR_TYPE_REDIST_REGION attributes.
 
+  Note that to obtain reproducible results (the same VCPU being associated
+  with the same redistributor across a save/restore operation), VCPU creation
+  order, redistributor region creation order as well as the respective
+  interleaves of VCPU and region creation MUST be preserved.  Any change in
+  either ordering may result in a different vcpu_id/redistributor association,
+  resulting in a VM that will fail to run at restore time.
+
   Errors:
 
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