Add some basic documentation on how to get feature ID register writable
masks from userspace.
Signed-off-by: Jing Zhang <jingzhangos@xxxxxxxxxx>
---
Documentation/virt/kvm/api.rst | 42 ++++++++++++++++++++++++++++++++++
1 file changed, 42 insertions(+)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 21a7578142a1..2defb5e198ce 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6070,6 +6070,48 @@ writes to the CNTVCT_EL0 and CNTPCT_EL0 registers using the SET_ONE_REG
interface. No error will be returned, but the resulting offset will not be
applied.
+4.139 KVM_ARM_GET_REG_WRITABLE_MASKS
+-------------------------------------------
+
+:Capability: KVM_CAP_ARM_SUPPORTED_FEATURE_ID_RANGES
+:Architectures: arm64
+:Type: vm ioctl
+:Parameters: struct reg_mask_range (in/out)
+:Returns: 0 on success, < 0 on error
+
+
+::
+
+ #define ARM64_FEATURE_ID_SPACE_SIZE (3 * 8 * 8)
+ #define ARM64_FEATURE_ID_RANGE_IDREGS BIT(0)
+
+ struct reg_mask_range {
+ __u64 addr; /* Pointer to mask array */
+ __u32 range; /* Requested range */
+ __u32 reserved[13];
+ };
+
+This ioctl copies the writable masks for Feature ID registers to userspace.
+The Feature ID space is defined as the AArch64 System register space with
+op0==3, op1=={0, 1, 3}, CRn==0, CRm=={0-7}, op2=={0-7}.
+
+The mask array pointed to by ``addr`` is indexed by the macro
+``ARM64_FEATURE_ID_SPACE_IDX(op0, op1, crn, crm, op2)``, allowing userspace
+to know what bits can be changed for the system register described by ``op0,
+op1, crn, crm, op2``.
+
+The ``range`` field describes the requested range of registers. The valid
+ranges can be retrieved by checking the return value of
+KVM_CAP_CHECK_EXTENSION_VM for the KVM_CAP_ARM_SUPPORTED_FEATURE_ID_RANGES
+capability, which will return a bitmask of the supported ranges. Each bit
+set in the return value represents a possible value for the ``range``
+field. At the time of writing, only bit 0 is returned set by the
+capability, meaning that only the value ``ARM64_FEATURE_ID_RANGE_IDREGS``
+is valid for ``range``.
+
+The ``reserved[13]`` array is reserved for future use and should be 0, or
+KVM may return an error.
+
5. The kvm_run structure
========================
--
2.42.0.459.ge4e396fd5e-goog
