The Arm SMCCC is rather prescriptive in regards to the allocation of SMCCC function ID ranges. Many of the hypercall ranges have an associated specification from Arm (FF-A, PSCI, SDEI, etc.) with some room for vendor-specific implementations. The ever-expanding SMCCC surface leaves a lot of work within KVM for providing new features. Furthermore, KVM implements its own vendor-specific ABI, with little room for other implementations (like Hyper-V, for example). Rather than cramming it all into the kernel we should provide a way for userspace to handle hypercalls. It would appear that vCPU hotplug [*] has a legitimate use case for something like this, sending PSCI calls to userspace (where they should have gone in the first place). [*] https://lore.kernel.org/kvmarm/20230203135043.409192-1-james.morse@xxxxxxx/ => We have these new hypercall bitmap registers, why not use that? The hypercall bitmap registers aren't necessarily aimed at the same problem. The bitmap registers allow a VMM to preserve the ABI the guest gets from KVM by default when migrating between hosts. By default KVM exposes the entire feature set to the guest, whereas user SMCCC calls need explicit opt-in from userspace. Applies to 6.3-rc3. RFCv2: https://lore.kernel.org/kvmarm/20230211013759.3556016-1-oliver.upton@xxxxxxxxx/ RFCv2 -> v1: - Redefine kvm_run::hypercall::longmode as a flags field (Sean) - Handle SMCs from EL1 - Pre-increment PC before exiting to userspace for an SMC - A test! Oliver Upton (11): KVM: x86: Redefine 'longmode' as a flag for KVM_EXIT_HYPERCALL KVM: arm64: Add a helper to check if a VM has ran once KVM: arm64: Add vm fd device attribute accessors KVM: arm64: Rename SMC/HVC call handler to reflect reality KVM: arm64: Start handling SMCs from EL1 KVM: arm64: Refactor hvc filtering to support different actions KVM: arm64: Use a maple tree to represent the SMCCC filter KVM: arm64: Add support for KVM_EXIT_HYPERCALL KVM: arm64: Indroduce support for userspace SMCCC filtering KVM: selftests: Add a helper for SMCCC calls with SMC instruction KVM: selftests: Add test for SMCCC filter Documentation/virt/kvm/api.rst | 24 ++- Documentation/virt/kvm/devices/vm.rst | 74 +++++++ arch/arm64/include/asm/kvm_host.h | 8 +- arch/arm64/include/uapi/asm/kvm.h | 24 +++ arch/arm64/kvm/arm.c | 35 ++++ arch/arm64/kvm/handle_exit.c | 22 +- arch/arm64/kvm/hypercalls.c | 155 +++++++++++++- arch/arm64/kvm/pmu-emul.c | 4 +- arch/x86/include/uapi/asm/kvm.h | 9 + arch/x86/kvm/x86.c | 5 +- include/kvm/arm_hypercalls.h | 6 +- include/uapi/linux/kvm.h | 9 +- tools/testing/selftests/kvm/Makefile | 1 + .../selftests/kvm/aarch64/smccc_filter.c | 196 ++++++++++++++++++ .../selftests/kvm/include/aarch64/processor.h | 13 ++ .../selftests/kvm/lib/aarch64/processor.c | 52 +++-- 16 files changed, 593 insertions(+), 44 deletions(-) create mode 100644 tools/testing/selftests/kvm/aarch64/smccc_filter.c base-commit: e8d018dd0257f744ca50a729e3d042cf2ec9da65 -- 2.40.0.rc1.284.g88254d51c5-goog
