[PATCH v8 0/8] KVM: arm64: Add idempotent controls to migrate guest counter

[Oliver Upton]

Currently, on KVM/arm64, we only allow a VMM to migrate the guest's
virtual counter by-value. Saving and restoring the counter by value is
problematic in the fact that the recorded state is not idempotent.
Furthermore, we obfuscate from userspace the fact that the architecture
actually provides offset-based controls.

Another issue is that KVM/arm64 doesn't provide userspace with the
controls of the physical counter-timer. This series aims to address both
issues by adding offset-based controls for the virtual and physical
counters.

Patches 1-2 are refactor changes required to provide offset controls to
userspace and putting in some generic plumbing to use for both physical
and virtual offsets.

Patch 3 is a minor refactor, creating a helper function to get the
number of timer registers for a particular vCPU.

Patch 4 exposes a vCPU's virtual offset through the KVM_*_ONE_REG
ioctls. When NV support is added to KVM, CNTVOFF_EL2 will be considered
a guest system register. So, it is safe to expose it now through that
ioctl.

Patch 5 adds a cpufeature bit to detect 'full' ECV implementations,
providing EL2 with the ability to offset the physical counter-timer.

Patch 6 exposes a vCPU's physical offset as a vCPU device attribute.
This is deliberate, as the attribute is not architectural; KVM uses this
attribute to track the host<->guest offset.

Patch 7 is a prepatory change for the sake of physical offset emulation,
as counter-timer traps must be configured separately for each vCPU.

Patch 8 allows non-ECV hosts to support the physical offset vCPU device
attribute, by trapping and emulating the physical counter registers.

This series was tested on an Ampere Mt. Jade system (non-ECV, VHE and
nVHE). I did not test this on the FVP, as I need to really figure out
tooling for it on my workstation.

Applies cleanly to v5.15-rc1

v7: http://lore.kernel.org/r/20210816001217.3063400-1-oupton@google.com

v7 -> v8:
 - Only use ECV if !VHE
 - Only expose CNTVOFF_EL2 register to userspace with opt-in
 - Refer to the direct_ptimer explicitly

Oliver Upton (8):
  KVM: arm64: Refactor update_vtimer_cntvoff()
  KVM: arm64: Separate guest/host counter offset values
  KVM: arm64: Make a helper function to get nr of timer regs
  KVM: arm64: Allow userspace to configure a vCPU's virtual offset
  arm64: cpufeature: Enumerate support for FEAT_ECV >= 0x2
  KVM: arm64: Allow userspace to configure a guest's counter-timer
    offset
  KVM: arm64: Configure timer traps in vcpu_load() for VHE
  KVM: arm64: Emulate physical counter offsetting on non-ECV systems

 Documentation/arm64/booting.rst         |   7 +
 Documentation/virt/kvm/api.rst          |  23 +++
 Documentation/virt/kvm/devices/vcpu.rst |  28 ++++
 arch/arm64/include/asm/kvm_host.h       |   3 +
 arch/arm64/include/asm/sysreg.h         |   5 +
 arch/arm64/include/uapi/asm/kvm.h       |   2 +
 arch/arm64/kernel/cpufeature.c          |  10 ++
 arch/arm64/kvm/arch_timer.c             | 196 +++++++++++++++++++++---
 arch/arm64/kvm/arm.c                    |   9 +-
 arch/arm64/kvm/guest.c                  |  28 +++-
 arch/arm64/kvm/hyp/include/hyp/switch.h |  32 ++++
 arch/arm64/kvm/hyp/nvhe/timer-sr.c      |  11 +-
 arch/arm64/tools/cpucaps                |   1 +
 include/clocksource/arm_arch_timer.h    |   1 +
 include/kvm/arm_arch_timer.h            |  14 +-
 include/uapi/linux/kvm.h                |   1 +
 16 files changed, 337 insertions(+), 34 deletions(-)

-- 
2.33.0.309.g3052b89438-goog