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From: Oliver Upton To: Jing Zhang Cc: KVM , KVMARM , ARMLinux , Marc Zyngier , Will Deacon , Paolo Bonzini , James Morse , Alexandru Elisei , Suzuki K Poulose , Fuad Tabba , Reiji Watanabe , Raghavendra Rao Ananta , Suraj Jitindar Singh , Cornelia Huck Subject: Re: [PATCH v7 01/10] KVM: arm64: Allow userspace to get the writable masks for feature ID registers Message-ID: References: <20230801152007.337272-1-jingzhangos@google.com> <20230801152007.337272-2-jingzhangos@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20230801152007.337272-2-jingzhangos@google.com> X-Migadu-Flow: FLOW_OUT X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230801_170502_830593_4D132FED X-CRM114-Status: GOOD ( 27.87 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Jing, On Tue, Aug 01, 2023 at 08:19:57AM -0700, Jing Zhang wrote: > Add a VM ioctl to allow userspace to get writable masks for feature ID > registers in below system register space: > op0 = 3, op1 = {0, 1, 3}, CRn = 0, CRm = {0 - 7}, op2 = {0 - 7} > This is used to support mix-and-match userspace and kernels for writable > ID registers, where userspace may want to know upfront whether it can > actually tweak the contents of an idreg or not. > > Suggested-by: Marc Zyngier > Suggested-by: Cornelia Huck > Signed-off-by: Jing Zhang > --- > arch/arm64/include/asm/kvm_host.h | 2 ++ > arch/arm64/include/uapi/asm/kvm.h | 25 +++++++++++++++ > arch/arm64/kvm/arm.c | 3 ++ > arch/arm64/kvm/sys_regs.c | 51 +++++++++++++++++++++++++++++++ > include/uapi/linux/kvm.h | 2 ++ > 5 files changed, 83 insertions(+) > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > index d3dd05bbfe23..3996a3707f4e 100644 > --- a/arch/arm64/include/asm/kvm_host.h > +++ b/arch/arm64/include/asm/kvm_host.h > @@ -1074,6 +1074,8 @@ int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm, > struct kvm_arm_copy_mte_tags *copy_tags); > int kvm_vm_ioctl_set_counter_offset(struct kvm *kvm, > struct kvm_arm_counter_offset *offset); > +int kvm_vm_ioctl_get_feature_id_writable_masks(struct kvm *kvm, > + u64 __user *masks); > > /* Guest/host FPSIMD coordination helpers */ > int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu); > diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h > index f7ddd73a8c0f..2970c0d792ee 100644 > --- a/arch/arm64/include/uapi/asm/kvm.h > +++ b/arch/arm64/include/uapi/asm/kvm.h > @@ -505,6 +505,31 @@ struct kvm_smccc_filter { > #define KVM_HYPERCALL_EXIT_SMC (1U << 0) > #define KVM_HYPERCALL_EXIT_16BIT (1U << 1) > > +/* Get feature ID registers userspace writable mask. */ > +/* > + * From DDI0487J.a, D19.2.66 ("ID_AA64MMFR2_EL1, AArch64 Memory Model > + * Feature Register 2"): > + * > + * "The Feature ID space is defined as the System register space in > + * AArch64 with op0==3, op1=={0, 1, 3}, CRn==0, CRm=={0-7}, > + * op2=={0-7}." > + * > + * This covers all R/O registers that indicate anything useful feature > + * wise, including the ID registers. > + */ > +#define ARM64_FEATURE_ID_SPACE_IDX(op0, op1, crn, crm, op2) \ > + ({ \ > + __u64 __op1 = (op1) & 3; \ > + __op1 -= (__op1 == 3); \ > + (__op1 << 6 | ((crm) & 7) << 3 | (op2)); \ > + }) > + > +#define ARM64_FEATURE_ID_SPACE_SIZE (3 * 8 * 8) > + > +struct feature_id_writable_masks { > + __u64 mask[ARM64_FEATURE_ID_SPACE_SIZE]; > +}; This UAPI is rather difficult to extend in the future. We may need to support describing the masks of multiple ranges of registers in the future. I was thinking something along the lines of: enum reg_mask_range_idx { FEATURE_ID, }; struct reg_mask_range { __u64 idx; __u64 *masks; __u64 rsvd[6]; }; > #endif > > #endif /* __ARM_KVM_H__ */ > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > index 72dc53a75d1c..c9cd14057c58 100644 > --- a/arch/arm64/kvm/arm.c > +++ b/arch/arm64/kvm/arm.c > @@ -1630,6 +1630,9 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg) > > return kvm_vm_set_attr(kvm, &attr); > } > + case KVM_ARM_GET_FEATURE_ID_WRITABLE_MASKS: { > + return kvm_vm_ioctl_get_feature_id_writable_masks(kvm, argp); > + } > default: > return -EINVAL; > } > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > index 2ca2973abe66..d9317b640ba5 100644 > --- a/arch/arm64/kvm/sys_regs.c > +++ b/arch/arm64/kvm/sys_regs.c > @@ -3560,6 +3560,57 @@ int kvm_arm_copy_sys_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices) > return write_demux_regids(uindices); > } > > +#define ARM64_FEATURE_ID_SPACE_INDEX(r) \ > + ARM64_FEATURE_ID_SPACE_IDX(sys_reg_Op0(r), \ > + sys_reg_Op1(r), \ > + sys_reg_CRn(r), \ > + sys_reg_CRm(r), \ > + sys_reg_Op2(r)) > + > +static bool is_feature_id_reg(u32 encoding) > +{ > + return (sys_reg_Op0(encoding) == 3 && > + (sys_reg_Op1(encoding) < 2 || sys_reg_Op1(encoding) == 3) && > + sys_reg_CRn(encoding) == 0 && > + sys_reg_CRm(encoding) <= 7); > +} > + > +int kvm_vm_ioctl_get_feature_id_writable_masks(struct kvm *kvm, u64 __user *masks) > +{ Use the correct type for the user pointer (it's a struct pointer). > + /* Wipe the whole thing first */ > + for (int i = 0; i < ARM64_FEATURE_ID_SPACE_SIZE; i++) > + if (put_user(0, masks + i)) > + return -EFAULT; Why not: if (clear_user(masks, ARM64_FEATURE_ID_SPACE_SIZE * sizeof(__u64))) return -EFAULT; Of course, this may need to be adapted if the UAPI struct changes. -- Thanks, Oliver _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel