On Thu, Jul 29, 2021 at 12:10:10AM +0000, Oliver Upton wrote:

Presently, KVM provides no facilities for correctly migrating a guest
that depends on the physical counter-timer. While most guests (barring
NV, of course) should not depend on the physical counter-timer, an
operator may still wish to provide a consistent view of the physical
counter-timer across migrations.

Provide userspace with a new vCPU attribute to modify the guest physical
counter-timer offset. Since the base architecture doesn't provide a
physical counter-timer offset register, emulate the correct behavior by
trapping accesses to the physical counter-timer whenever the offset
value is non-zero.

Uphold the same behavior as CNTVOFF_EL2 and broadcast the physical
offset to all vCPUs whenever written. This guarantees that the
counter-timer we provide the guest remains architectural, wherein all
views of the counter-timer are consistent across vCPUs. Reconfigure
timer traps for VHE on every guest entry, as different VMs will now have
different traps enabled. Enable physical counter traps for nVHE whenever
the offset is nonzero (we already trap physical timer registers in
nVHE).

FEAT_ECV provides a guest physical counter-timer offset register
(CNTPOFF_EL2), but ECV-enabled hardware is nonexistent at the time of
writing so support for it was elided for the sake of the author :)

Cc: Andrew Jones <redacted>
Signed-off-by: Oliver Upton <redacted>
---
 Documentation/virt/kvm/devices/vcpu.rst   | 22 +++++++
 arch/arm64/include/asm/kvm_host.h         |  1 +
 arch/arm64/include/asm/kvm_hyp.h          |  2 -
 arch/arm64/include/asm/sysreg.h           |  1 +
 arch/arm64/include/uapi/asm/kvm.h         |  1 +
 arch/arm64/kvm/arch_timer.c               | 72 ++++++++++++++---------
 arch/arm64/kvm/arm.c                      |  4 +-
 arch/arm64/kvm/hyp/include/hyp/switch.h   | 23 ++++++++
 arch/arm64/kvm/hyp/include/hyp/timer-sr.h | 26 ++++++++
 arch/arm64/kvm/hyp/nvhe/switch.c          |  2 -
 arch/arm64/kvm/hyp/nvhe/timer-sr.c        | 21 +++----
 arch/arm64/kvm/hyp/vhe/timer-sr.c         | 27 +++++++++
 include/kvm/arm_arch_timer.h              |  2 -
 13 files changed, 158 insertions(+), 46 deletions(-)
 create mode 100644 arch/arm64/kvm/hyp/include/hyp/timer-sr.h

 
Reviewed-by: Andrew Jones <redacted>


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