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KVM: arm64: Document KVM_ARM_GET_REG_WRITABLE_MASKS 

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
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
========================