[PATCH v8 01/11] KVM: arm64: Allow userspace to get the writable masks for feature ID registers
Jing Zhang
jingzhangos at google.com
Mon Aug 7 09:21:59 PDT 2023
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 <maz at kernel.org>
Suggested-by: Cornelia Huck <cohuck at redhat.com>
Signed-off-by: Jing Zhang <jingzhangos at google.com>
---
arch/arm64/include/asm/kvm_host.h | 2 ++
arch/arm64/include/uapi/asm/kvm.h | 26 ++++++++++++++
arch/arm64/kvm/arm.c | 7 ++++
arch/arm64/kvm/sys_regs.c | 57 +++++++++++++++++++++++++++++++
include/uapi/linux/kvm.h | 1 +
5 files changed, 93 insertions(+)
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index d3dd05bbfe23..a328d362df5a 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_reg_writable_masks(struct kvm *kvm,
+ struct reg_mask_range *range);
/* 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..7a21bbb8a0f7 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -505,6 +505,32 @@ 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 reg_mask_range {
+ __u64 addr; /* Pointer to mask array */
+ __u64 reserved[7];
+};
+
#endif
#endif /* __ARM_KVM_H__ */
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 72dc53a75d1c..e08894692829 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1630,6 +1630,13 @@ 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_REG_WRITABLE_MASKS: {
+ struct reg_mask_range range;
+
+ if (copy_from_user(&range, argp, sizeof(range)))
+ return -EFAULT;
+ return kvm_vm_ioctl_get_reg_writable_masks(kvm, &range);
+ }
default:
return -EINVAL;
}
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 2ca2973abe66..216905840c92 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -3560,6 +3560,63 @@ 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_reg_writable_masks(struct kvm *kvm, struct reg_mask_range *range)
+{
+ const void *zero_page = page_to_virt(ZERO_PAGE(0));
+ u64 __user *masks = (u64 __user *)range->addr;
+
+ /* Only feature id range is supported, reserved[7] must be zero. */
+ if (memcmp(range->reserved, zero_page, sizeof(range->reserved)))
+ return -EINVAL;
+
+ /* Wipe the whole thing first */
+ if (clear_user(masks, ARM64_FEATURE_ID_SPACE_SIZE * sizeof(__u64)))
+ return -EFAULT;
+
+ for (int i = 0; i < ARRAY_SIZE(sys_reg_descs); i++) {
+ const struct sys_reg_desc *reg = &sys_reg_descs[i];
+ u32 encoding = reg_to_encoding(reg);
+ u64 val;
+
+ if (!is_feature_id_reg(encoding) || !reg->set_user)
+ continue;
+
+ /*
+ * For ID registers, we return the writable mask. Other feature
+ * registers return a full 64bit mask. That's not necessary
+ * compliant with a given revision of the architecture, but the
+ * RES0/RES1 definitions allow us to do that.
+ */
+ if (is_id_reg(encoding)) {
+ if (!reg->val)
+ continue;
+ val = reg->val;
+ } else {
+ val = ~0UL;
+ }
+
+ if (put_user(val, (masks + ARM64_FEATURE_ID_SPACE_INDEX(encoding))))
+ return -EFAULT;
+ }
+
+ return 0;
+}
+
int __init kvm_sys_reg_table_init(void)
{
struct sys_reg_params params;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index f089ab290978..424b6d00440b 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1555,6 +1555,7 @@ struct kvm_s390_ucas_mapping {
#define KVM_ARM_MTE_COPY_TAGS _IOR(KVMIO, 0xb4, struct kvm_arm_copy_mte_tags)
/* Available with KVM_CAP_COUNTER_OFFSET */
#define KVM_ARM_SET_COUNTER_OFFSET _IOW(KVMIO, 0xb5, struct kvm_arm_counter_offset)
+#define KVM_ARM_GET_REG_WRITABLE_MASKS _IOR(KVMIO, 0xb6, struct reg_mask_range)
/* ioctl for vm fd */
#define KVM_CREATE_DEVICE _IOWR(KVMIO, 0xe0, struct kvm_create_device)
--
2.41.0.585.gd2178a4bd4-goog
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