As discussed at KVM Forum, this series introduces documentation for the
"VM planes" concept that can be used to implement at least AMD VMPLs
and Microsoft VTLs.
I didn't include Intel TDX and Arm CCA, because people expressed doubts
on whether KVM could deal with {firm,hard}ware that magically enters the
vCPU in one privilege level and leave at another. This however may not
be a blocker, especially considering that we decided to have only one
mutex for all planes.
Compared to the notes from the KVM Forum BoF, the main change is in the
kvm_run fields. The design at the BoF had fields masked_planes and
runnable_planes, and a userspace exit would happen if the value of
runnable_planes & ~masked_planes became nonzero.
Here instead I have:
- req_exit_planes which is similar to ~masked_planes. The difference comes
from the Hyper-V VINA feature ("Virtual Interrupt Notification Assist"),
which requires userspace to know about _all_ interrupts, even those for
lower VTLs
- suspended_planes, which is not used yet but needs to be there for future
in-kernel accelerations, because interrupts can "skip" VTLs/VMPLs and need
to return to the last suspended level.
I am not sure that this needs to be in kvm_run though. It definitely has
to be migrated once KVM supports in-kernel switch, but I am not sure that
userspace needs it "enough" to put it in kvm_run. It could be accessed
with KVM_GET_ONE_REG/KVM_SET_ONE_REG or similar, perhaps.
- pending_event_planes (same as runnable_planes) is in the KVM_EXIT_PLANE_EVENT
data, kvm_run->exit.plane. It seems that it is not used in any other case
by userspace (KVM probably needs to keep it up to date at all time; but
it cannot trust anyway what is in kvm_run and needs to have its own copy).
Another difference is in whether FPU is shared. We had it as shared,
but for SEV-ES the contents of the x87 and AVX registers are stored in
the VMSA and therefore each VMPL has its own copy. The solution I have
(KVM_CAP_PLANE_FPU) is a bit of a cop out though.
In order to add the relevant text, there are a few cleanups that can be applied
separately.
Paolo Bonzini (5):
KVM: powerpc: remove remaining traces of KVM_CAP_PPC_RMA
Documentation: kvm: fix a few mistakes
Documentation: kvm: replace section numbers with links
Documentation: kvm: reorganize introduction
Documentation: kvm: introduce "VM plane" concept
Documentation/virt/kvm/api.rst | 357 ++++++++++++++++-------
Documentation/virt/kvm/vcpu-requests.rst | 7 +
arch/powerpc/kvm/powerpc.c | 3 -
3 files changed, 266 insertions(+), 101 deletions(-)
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2.46.2
