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 | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index c0ddd3035462..e6cda4169764 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6068,6 +6068,32 @@ 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_FEATURE_ID_WRITABLE_MASKS
+-------------------------------------------
+
+:Capability: none
+:Architectures: arm64
+:Type: vm ioctl
+:Parameters: struct feature_id_writable_masks (out)
+:Returns: 0 on success, < 0 on error
+
+
+::
+
+ #define ARM64_FEATURE_ID_SPACE_SIZE (3 * 8 * 8)
+
+ struct feature_id_writable_masks {
+ __u64 mask[ARM64_FEATURE_ID_SPACE_SIZE];
+ };
+
+This ioctl would copy the writable masks for feature ID registers to userspace.
+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}.
+To get the index in ``mask`` array for a specified feature ID register, use the
+macro ``ARM64_FEATURE_ID_SPACE_IDX(op0, op1, crn, crm, op2)``.
+This allows the userspace to know upfront whether it can actually tweak the
+contents of a feature ID register or not.
+
5. The kvm_run structure
========================
--
2.41.0.585.gd2178a4bd4-goog
