Hi Reiji, On Tue, Nov 23, 2021 at 09:49:02PM -0800, Reiji Watanabe wrote: > Hi Alex, > > On Tue, Nov 23, 2021 at 8:25 AM Alexandru Elisei > <alexandru.elisei@xxxxxxx> wrote: > > > > Hi Reiji, > > > > The API documentation for KVM_ARM_VCPU_INIT states: > > > > "Userspace can call this function multiple times for a given vcpu, > > including after the vcpu has been run. This will reset the vcpu to its > > initial state. All calls to this function after the initial call must use > > the same target and same set of feature flags, otherwise EINVAL will be > > returned." > > > > The consequences of that, according to my understanding: > > > > 1. Any changes to the VCPU features made by KVM are observable by > > userspace. > > > > 2. The features in KVM weren't designed and implemented to be disabled > > after being enabled. > > > > With that in mind, I have two questions: > > > > 1. What happens when userspace disables a feature via the ID registers > > which is set in vcpu->arch.features? Does the feature bit get cleared from > > vcpu->arch.features? Does it stay set? If it gets cleared, is it now > > possible for userspace to call KVM_ARM_VCPU_INIT again with a different set > > of VCPU features (it doesn't look possible to me after looking at the > > code). If it stays set, what does it mean when userspace calls > > KVM_ARM_VCPU_INIT with a different set of features enabled than what is > > present in the ID registers? Should the ID registers be changed to match > > the features that userspace set in the last KVM_ARM_VCPU_INIT call (it > > looks to me that the ID registers are not changed)? > > KVM will not allow userspace to set the ID register value that conflicts > with CPU features that are configured by the initial KVM_ARM_VCPU_INIT > (or there are a few more APIs). > KVM_SET_ONE_REG for such requests will fail. > > > > 2. What happens to vcpu->arch.features when userspace enables a feature via > > the ID registers which is not present in the bitmap? > > The answer for this question is basically the same as above. > Userspace is not allowed to enable a feature via the ID registers > which is not present in the bit map. > > The cover lever included a brief explanation of this, but I will > try to improve the explanation:-) So the ID registers are used to set the version of a feature which is present in the VCPU features bitmap, not to enable or a disable a VCPU feature. Thank you for the explanation! Thanks, Alex > > Regards, > Reiji > > > > > Thanks, > > Alex > > > > On Tue, Nov 16, 2021 at 10:43:30PM -0800, Reiji Watanabe wrote: > > > 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 is for both VHE and non-VHE, except for protected VMs, > > > which have a different way of configuring ID registers based on its > > > different requirements [1]. > > > 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]. > > > > > > The initial value of ID registers for a vCPU will be the host's value > > > with bits cleared for unsupported features and for opt-in features that > > > were not configured. So, 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 is 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. > > > > > > This series adds kunit tests for new functions in sys_regs.c (except for > > > trivial ones), and these tests are enabled with a new configuration > > > option 'CONFIG_KVM_KUNIT_TEST'. > > > > > > The series is based on v5.16-rc1. > > > > > > v3: > > > - Remove ID register consistency checking across vCPUs [Oliver] > > > - Change KVM_CAP_ARM_ID_REG_WRITABLE to > > > KVM_CAP_ARM_ID_REG_CONFIGURABLE [Oliver] > > > - Add KUnit testing for ID register validation and trap initialization. > > > - Change read_id_reg() to take care of ID_AA64PFR0_EL1.GIC > > > - Add a helper of read_id_reg() (__read_id_reg()) and use the helper > > > instead of directly using __vcpu_sys_reg() > > > - Change not to run kvm_id_regs_consistency_check() and > > > kvm_vcpu_init_traps() for protected VMs. > > > - Update selftest to remove test cases for ID register consistency > > > checking across vCPUs and to add test cases for ID_AA64PFR0_EL1.GIC. > > > > > > v2: https://lore.kernel.org/all/20211103062520.1445832-1-reijiw@xxxxxxxxxx/ > > > - Remove unnecessary line breaks. [Andrew] > > > - Use @params for comments. [Andrew] > > > - Move arm64_check_features to arch/arm64/kvm/sys_regs.c and > > > change that KVM specific feature check function. [Andrew] > > > - Remove unnecessary raz handling from __set_id_reg. [Andrew] > > > - Remove sys_val field from the initial id_reg_info and add it > > > in the later patch. [Andrew] > > > - Call id_reg->init() from id_reg_info_init(). [Andrew] > > > - Fix cpuid_feature_cap_perfmon_field() to convert 0xf to 0x0 > > > (and use it in the following patches). > > > - Change kvm_vcpu_first_run_init to set has_run_once to false > > > when kvm_id_regs_consistency_check() fails. > > > - Add a patch to introduce id_reg_info for ID_AA64MMFR0_EL1, > > > which requires special validity checking for TGran*_2 fields. > > > - Add patches to introduce id_reg_info for ID_DFR1_EL1 and > > > ID_MMFR0_EL1, which are required due to arm64_check_features > > > implementation change. > > > - Add a new argument, which is a pointer to id_reg_info, for > > > id_reg_info's validate() > > > > > > v1: https://lore.kernel.org/all/20211012043535.500493-1-reijiw@xxxxxxxxxx/ > > > > > > [1] https://lore.kernel.org/kvmarm/20211010145636.1950948-1-tabba@xxxxxxxxxx/ > > > [2] https://lore.kernel.org/kvm/20201102033422.657391-1-liangpeng10@xxxxxxxxxx/ > > > > > > Reiji Watanabe (29): > > > KVM: arm64: Add has_reset_once flag for vcpu > > > KVM: arm64: Save ID registers' sanitized value per vCPU > > > KVM: arm64: Introduce struct id_reg_info > > > 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_AA64MMFR0_EL1 writable > > > KVM: arm64: Hide IMPLEMENTATION DEFINED PMU support for the guest > > > KVM: arm64: Make ID_AA64DFR0_EL1 writable > > > KVM: arm64: Make ID_DFR0_EL1 writable > > > KVM: arm64: Make ID_DFR1_EL1 writable > > > KVM: arm64: Make ID_MMFR0_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_CONFIGURABLE capability > > > KVM: arm64: Add kunit test for ID register validation > > > 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: Initialize trapping of disabled CPU features for the guest > > > KVM: arm64: Add kunit test for trap initialization > > > KVM: arm64: selftests: Introduce id_reg_test > > > > > > Documentation/virt/kvm/api.rst | 8 + > > > arch/arm64/include/asm/cpufeature.h | 2 +- > > > arch/arm64/include/asm/kvm_arm.h | 32 + > > > arch/arm64/include/asm/kvm_host.h | 15 + > > > arch/arm64/include/asm/sysreg.h | 2 + > > > arch/arm64/kvm/Kconfig | 11 + > > > arch/arm64/kvm/arm.c | 12 +- > > > 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 | 1265 +++++++++++++++-- > > > arch/arm64/kvm/sys_regs_test.c | 1109 +++++++++++++++ > > > 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 | 1128 +++++++++++++++ > > > 17 files changed, 3488 insertions(+), 131 deletions(-) > > > create mode 100644 arch/arm64/kvm/sys_regs_test.c > > > create mode 100644 tools/testing/selftests/kvm/aarch64/id_reg_test.c > > > > > > -- > > > 2.34.0.rc1.387.gb447b232ab-goog > > > _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
