For reasons unknown, the Arm architecture defines the 64-bit views of the 32-bit ID registers as UNKNOWN [1]. This combines poorly with the fact that KVM unconditionally exposes these registers to userspace, which could throw a wrench in migration between 64-bit only systems. This series reworks KVM's definition of these registers to RAZ/WI with the goal of providing consistent register values across 64-bit machines. Patches 1-2 clean up some of the ID register accessors, taking advantage of the fact that the generic ones already know how to handle RAZ registers. Patches 3-4 wire in a new visibility bit to indicate a register ignores writes from userspace. Patch 5 moves all exposed 32-bit ID registers to have RAZ/WI behavior on 64-bit only systems. Note that hidden 32-bit registers continue to have RAZ behavior and carry the additional requirement of invariance. Lastly, patch 6 tests that userspace and guest indeed see the registers as RAZ/WI. Applies to 6.0-rc1 + the mismatched system fixes [2] picked up earlier today. Tested on the fast model, both with mismatched AArch32 support and no AArch32 support whatoever. [1]: DDI0487H.a Table D12-2 'Instruction encodings for non-Debug System Register accesses' [2]: https://lore.kernel.org/kvmarm/20220816192554.1455559-1-oliver.upton@xxxxxxxxx/ Oliver Upton (6): KVM: arm64: Use visibility hook to treat ID regs as RAZ KVM: arm64: Remove internal accessor helpers for id regs KVM: arm64: Spin off helper for calling visibility hook KVM: arm64: Add a visibility bit to ignore user writes KVM: arm64: Treat 32bit ID registers as RAZ/WI on 64bit-only system KVM: selftests: Add test for RAZ/WI AArch32 ID registers arch/arm64/kvm/sys_regs.c | 137 +++++++++--------- arch/arm64/kvm/sys_regs.h | 24 ++- tools/testing/selftests/kvm/.gitignore | 1 + tools/testing/selftests/kvm/Makefile | 1 + .../kvm/aarch64/aarch64_only_id_regs.c | 135 +++++++++++++++++ 5 files changed, 222 insertions(+), 76 deletions(-) create mode 100644 tools/testing/selftests/kvm/aarch64/aarch64_only_id_regs.c -- 2.37.1.595.g718a3a8f04-goog _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
