In KVM/arm64, values of ID registers for a guest are mostly same as its host's values except for bits for feature that KVM doesn't support and for opt-in features that userspace didn't configure. Userspace can use KVM_SET_ONE_REG to a set ID register value, but it fails if userspace attempts to modify the register value. This patch series adds support to allow userspace to modify a value of ID registers (as long as KVM can support features that are indicated in the registers) so userspace can have more control of configuring and unconfiguring features for guests. The patch series affects both VHE or non-VHE including protected VMs for now but should be changed not to affect for protected VMs, which will have a different way of configuring ID registers [1] based on its different requirements. There was a patch series that tried to achieve the same thing [2]. A few snippets of codes in this series were inspired by or came from [2]. Since an initial value of ID registers will be the host value with bits cleared for unsupported features and for opt-in features that were not configured, the initial value userspace can see (via KVM_GET_ONE_REG) is the upper limit that can be set for the register. Any requests to change the value that conflicts with opt-in features' configuration will fail. When a guest tries to use a CPU feature that is not exposed to the guest, trapping it (to emulate a real CPU's behavior) would generally be a desirable behavior (when it's possible with no or little side effects). The later patches in the series add codes for this. Only features that can be trapped independently will be trapped by this series though. The series is based on 5.15-rc5 with the patch series [3] applied. Patch 01 introduces 'has_reset_once' flag for a vCPU to indicate if the vCPU reset has been done once. This is used to initialize ID registers only at the first vCPU reset. Patch 02 extends sys_regs[] of kvm_cpu_context to save values of ID registers for the vCPU. For now, the sanitized host's values are saved in the array at the first vCPU reset. Patch 03 introduces arm64_check_features(), which will do a common validation checking for ID registers. Patch 04 introduces structure id_reg_info to manage the ID register specific control of the register value for the guest. Patch 05 introduces a function to keep consistency of ID register values between vCPUs at the first KVM_RUN. Also, the patch adds code to prevent userspace from changing ID register value after the first KVM_RUN. Patches 06-12 add id_reg_info for ID registers to make them writable with some specific handling for the registers. Patch 13 changes KVM_SET_ONE_REG behavior for ID registers to allow userspace to change ID registers that don't have id_reg_info. Patch 14 introduces validity checking of feature fractional fields of ID registers at the first KVM_RUN. Patch 15 introduces a new capability KVM_CAP_ARM_ID_REG_WRITABLE to identify that ID registers are writable by userspace. Patches 16-17 changes the way of using vcpu->arch.cptr_el2/mdcr_el2 to track certain bits of cptr_el2/mdcr_el2 in the vcpu->arch fields and use them when setting them for the guest. The following patches will update the vcpu->arch fields based on available features for the guest. Patch 18 introduces struct feature_config_ctrl and some utility functions to enable trapping of features that are disabled for a guest. Patches 19-23 add feature_config_ctrl for CPU features, which are used to program configuration registers to trap each feature. Patch 24 enables trapping CPU features that are disabled for the guest based on feature_config_ctrl that were added by patch 18-23. Patch 25 adds a selftest to validate reading/writing ID registers. [1] https://lore.kernel.org/kvmarm/20211010145636.1950948-1-tabba@xxxxxxxxxx/ [2] https://lore.kernel.org/kvm/20201102033422.657391-1-liangpeng10@xxxxxxxxxx/ [3] https://lore.kernel.org/kvmarm/20211007233439.1826892-1-rananta@xxxxxxxxxx/ Reiji Watanabe (25): KVM: arm64: Add has_reset_once flag for vcpu KVM: arm64: Save ID registers' sanitized value per vCPU KVM: arm64: Introduce a validation function for an ID register KVM: arm64: Introduce struct id_reg_info KVM: arm64: Keep consistency of ID registers between vCPUs KVM: arm64: Make ID_AA64PFR0_EL1 writable KVM: arm64: Make ID_AA64PFR1_EL1 writable KVM: arm64: Make ID_AA64ISAR0_EL1 writable KVM: arm64: Make ID_AA64ISAR1_EL1 writable KVM: arm64: Make ID_AA64DFR0_EL1 writable KVM: arm64: Make ID_DFR0_EL1 writable KVM: arm64: Make MVFR1_EL1 writable KVM: arm64: Make ID registers without id_reg_info writable KVM: arm64: Add consistency checking for frac fields of ID registers KVM: arm64: Introduce KVM_CAP_ARM_ID_REG_WRITABLE capability KVM: arm64: Use vcpu->arch cptr_el2 to track value of cptr_el2 for VHE KVM: arm64: Use vcpu->arch.mdcr_el2 to track value of mdcr_el2 KVM: arm64: Introduce framework to trap disabled features KVM: arm64: Trap disabled features of ID_AA64PFR0_EL1 KVM: arm64: Trap disabled features of ID_AA64PFR1_EL1 KVM: arm64: Trap disabled features of ID_AA64DFR0_EL1 KVM: arm64: Trap disabled features of ID_AA64MMFR1_EL1 KVM: arm64: Trap disabled features of ID_AA64ISAR1_EL1 KVM: arm64: Activate trapping of disabled CPU features for the guest KVM: arm64: selftests: Introduce id_reg_test Documentation/virt/kvm/api.rst | 8 + arch/arm64/include/asm/cpufeature.h | 1 + arch/arm64/include/asm/kvm_arm.h | 32 + arch/arm64/include/asm/kvm_host.h | 18 +- arch/arm64/include/asm/sysreg.h | 1 + arch/arm64/kernel/cpufeature.c | 26 + arch/arm64/kvm/arm.c | 30 +- arch/arm64/kvm/debug.c | 13 +- arch/arm64/kvm/hyp/vhe/switch.c | 14 +- arch/arm64/kvm/reset.c | 4 + arch/arm64/kvm/sys_regs.c | 1010 +++++++++++-- include/uapi/linux/kvm.h | 1 + tools/arch/arm64/include/asm/sysreg.h | 1 + tools/testing/selftests/kvm/.gitignore | 1 + tools/testing/selftests/kvm/Makefile | 1 + .../selftests/kvm/aarch64/id_reg_test.c | 1296 +++++++++++++++++ 16 files changed, 2306 insertions(+), 151 deletions(-) create mode 100644 tools/testing/selftests/kvm/aarch64/id_reg_test.c -- 2.33.0.882.g93a45727a2-goog
