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KVM: arm64: Document KVM_ARM_GET_REG_WRITABLE_MASKS

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Add some basic documentation on how to get feature ID register writable
masks from userspace.

Signed-off-by: Jing Zhang <jingzhangos@google.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20231003230408.3405722-3-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
This commit is contained in:
Jing Zhang 2023-10-03 23:03:58 +00:00 committed by Oliver Upton
parent 3f9cd0ca84
commit 6656cda0f3
1 changed files with 48 additions and 0 deletions
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48
Documentation/virt/kvm/api.rst
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@ -6070,6 +6070,54 @@ 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 interface. No error will be returned, but the resulting offset will not be
applied. applied.
4.139 KVM_ARM_GET_REG_WRITABLE_MASKS
-------------------------------------------
:Capability: KVM_CAP_ARM_SUPPORTED_REG_MASK_RANGES
:Architectures: arm64
:Type: vm ioctl
:Parameters: struct reg_mask_range (in/out)
:Returns: 0 on success, < 0 on error
::
#define KVM_ARM_FEATURE_ID_RANGE 0
#define KVM_ARM_FEATURE_ID_RANGE_SIZE (3 * 8 * 8)
struct reg_mask_range {
__u64 addr; /* Pointer to mask array */
__u32 range; /* Requested range */
__u32 reserved[13];
};
This ioctl copies the writable masks for a selected range of registers to
userspace.
The ``addr`` field is a pointer to the destination array where KVM copies
the writable masks.
The ``range`` field indicates the requested range of registers.
``KVM_CHECK_EXTENSION`` for the ``KVM_CAP_ARM_SUPPORTED_REG_MASK_RANGES``
capability returns the supported ranges, expressed as a set of flags. Each
flag's bit index represents a possible value for the ``range`` field.
All other values are reserved for future use and KVM may return an error.
The ``reserved[13]`` array is reserved for future use and should be 0, or
KVM may return an error.
KVM_ARM_FEATURE_ID_RANGE (0)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The Feature ID range 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 returned array pointed to by ``addr`` is indexed by the macro
``ARM64_FEATURE_ID_RANGE_IDX(op0, op1, crn, crm, op2)``, allowing userspace
to know what fields can be changed for the system register described by
``op0, op1, crn, crm, op2``. KVM rejects ID register values that describe a
superset of the features supported by the system.
5. The kvm_run structure 5. The kvm_run structure
======================== ========================