[PATCH v4 0/6] KVM: arm64: emulation for CTR_EL0

[Sebastian Ott]

Hej folks,

I'm looking into supporting migration between 2 Ampere Altra (Max)
machines (using Neoverse-N1). They are almost identical regarding
their feature id register state except for CTR_EL0.DIC which is set
on one machine but not the other.

CTR_EL0 is currently marked as invariant and migrating a VM between
those 2 machines using qemu fails.

Changes RFC [0] -> V1 [1]:
 * store the emulated value per VM and not per VCPU
 * allow to change more values than just the DIC bit
 * only trap guest access to that reg when needed
 * make sure to not present the guest with an inconsistent register set
Changes V1 -> V2 [2]:
 * implemented Marc's suggestion for keeping registers consistent while
   not breaking userspace ABI / expectations (I hope correctly this time)
 * keep the shadowed value valid at all time
 * unify the code to setup traps
Changes V2 -> V3 [3]:
 * rebased to kvm-arm-next (to include Olivers idreg fixes)
 * fixed VM ops trapping for non-FWB CPUs
 * fixed writable mask for CLIDR_EL1
 * re-added manual ctr validation (using arm64_check_features() had a
   side effect with the way .reset is working for these registers)
 * added a testcase
Changes V3 -> V4:
 * incorporated feedback from Shaoqin and Eric

Thanks,
Sebastian

[0]: https://lore.kernel.org/all/20240318111636.10613-1-sebott@redhat.com/T/
[1]: https://lore.kernel.org/lkml/20240405120108.11844-1-sebott@redhat.com/T/
[2]: https://lore.kernel.org/lkml/20240426104950.7382-1-sebott@redhat.com/T/
[3]: https://lore.kernel.org/lkml/20240514072252.5657-1-sebott@redhat.com/T/

Sebastian Ott (6):
  KVM: arm64: unify code to prepare traps
  KVM: arm64: maintain per VM value for CTR_EL0
  KVM: arm64: add emulation for CTR_EL0 register
  KVM: arm64: show writable masks for feature registers
  KVM: arm64: rename functions for invariant sys regs
  KVM: selftests: arm64: Test writes to CTR_EL0

 arch/arm64/include/asm/kvm_emulate.h          |  40 +---
 arch/arm64/include/asm/kvm_host.h             |   4 +-
 arch/arm64/kvm/arm.c                          |   2 +-
 arch/arm64/kvm/sys_regs.c                     | 214 ++++++++++++++----
 .../selftests/kvm/aarch64/set_id_regs.c       |  16 ++
 5 files changed, 201 insertions(+), 75 deletions(-)

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2.42.0