[PATCH v6 4/4] RISC-V: KVM: add KVM_CAP_RISCV_SET_HGATP_MODE

fangyu.yu
2026-03-30T12:26:53Z

From: Fangyu Yu <fangyu.yu@linux.alibaba.com>

Add a VM capability that allows userspace to select the G-stage page table
format by setting HGATP.MODE on a per-VM basis.

Userspace enables the capability via KVM_ENABLE_CAP, passing the requested
HGATP.MODE in args[0]. The request is rejected with -EINVAL if the mode is
not supported by the host, and with -EBUSY if the VM has already been
committed (e.g. vCPUs have been created or any memslot is populated).

KVM_CHECK_EXTENSION(KVM_CAP_RISCV_SET_HGATP_MODE) returns a bitmask of the
HGATP.MODE formats supported by the host.

Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
Reviewed-by: Andrew Jones <andrew.jones@oss.qualcomm.com>
---
Documentation/virt/kvm/api.rst | 27 +++++++++++++++++++++++++++
arch/riscv/kvm/vm.c | 18 ++++++++++++++++--
include/uapi/linux/kvm.h | 1 +
3 files changed, 44 insertions(+), 2 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 032516783e96..9d7f6958fa81 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -8902,6 +8902,33 @@ helpful if user space wants to emulate instructions which are not
This capability can be enabled dynamically even if VCPUs were already
created and are running.

+7.47 KVM_CAP_RISCV_SET_HGATP_MODE
+---------------------------------
+
+:Architectures: riscv
+:Type: VM
+:Parameters: args[0] contains the requested HGATP mode
+:Returns:
+ - 0 on success.
+ - -EINVAL if args[0] is outside the range of HGATP modes supported by the
+ hardware.
+ - -EBUSY if vCPUs have already been created for the VM, if the VM has any
+ non-empty memslots.
+
+This capability allows userspace to explicitly select the HGATP mode for
+the VM. The selected mode must be supported by both KVM and hardware. This
+capability must be enabled before creating any vCPUs or memslots.
+
+If this capability is not enabled, KVM will select the default HGATP mode
+automatically. The default is the highest HGATP.MODE value supported by
+hardware.
+
+``KVM_CHECK_EXTENSION(KVM_CAP_RISCV_SET_HGATP_MODE)`` returns a bitmask of
+HGATP.MODE values supported by the host. A return value of 0 indicates that
+the capability is not supported. Supported-mode bitmask use HGATP.MODE
+encodings as defined by the RISC-V privileged specification, such as Sv39x4
+corresponds to HGATP.MODE=8, so userspace should test bitmask & BIT(8).
+
8. Other capabilities.
======================

diff --git a/arch/riscv/kvm/vm.c b/arch/riscv/kvm/vm.c
index 4d82a886102c..5e82a3ad3ad0 100644
--- a/arch/riscv/kvm/vm.c
+++ b/arch/riscv/kvm/vm.c
@@ -201,6 +201,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_VM_GPA_BITS:
r = kvm_riscv_gstage_gpa_bits(kvm->arch.pgd_levels);
break;
+ case KVM_CAP_RISCV_SET_HGATP_MODE:
+ r = kvm_riscv_get_hgatp_mode_mask();
+ break;
default:
r = 0;
break;
@@ -211,12 +214,23 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)

int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
{
+ if (cap->flags)
+ return -EINVAL;
+
switch (cap->cap) {
case KVM_CAP_RISCV_MP_STATE_RESET:
- if (cap->flags)
- return -EINVAL;
kvm->arch.mp_state_reset = true;
return 0;
+ case KVM_CAP_RISCV_SET_HGATP_MODE:
+ if (!kvm_riscv_hgatp_mode_is_valid(cap->args[0]))
+ return -EINVAL;
+
+ if (kvm->created_vcpus || !kvm_are_all_memslots_empty(kvm))
+ return -EBUSY;
+#ifdef CONFIG_64BIT
+ kvm->arch.pgd_levels = 3 + cap->args[0] - HGATP_MODE_SV39X4;
+#endif
+ return 0;
default:
return -EINVAL;
}
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 80364d4dbebb..a74a80fd4046 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -989,6 +989,7 @@ struct kvm_enable_cap {
#define KVM_CAP_ARM_SEA_TO_USER 245
#define KVM_CAP_S390_USER_OPEREXEC 246
#define KVM_CAP_S390_KEYOP 247
+#define KVM_CAP_RISCV_SET_HGATP_MODE 248

struct kvm_irq_routing_irqchip {
__u32 irqchip;
--
2.50.1