[PATCH 40/43] Documentation: KVM: Document KVM_DEV_ARM_VGIC_GRP_CPU_SYSREGS for VGICv5

[Sascha Bischoff <Sascha.Bischoff@arm.com>]

The virtual GICv5 adopts the same mechanism as GICv3 for userspace
read and writes of the system registers, albeit operating on a
different set of registers, of course.

Document KVM_DEV_ARM_VGIC_GRP_CPU_SYSREGS for GICv5 in the VGICv5
documentation, explicitly calling out the registers it operates
on. The main body of documentation has been directly copied from the
VGICv3 documentation as it has identical operation.

One key thing to note is that for two sets of GICv5 registers - those
pertaining to Active and Pending state - the operation of the
interface is different to how the actual registers operate. Both of
these registers have C and S variants (to set and clear bits) in
hardware. However for this interface, we ONLY implement the S variant,
AND treat it as a raw write. This simplifies the act of reading or
writing the state.

Signed-off-by: Sascha Bischoff <sascha.bischoff@arm.com>
---
 .../virt/kvm/devices/arm-vgic-v5.rst          | 66 +++++++++++++++++++
 1 file changed, 66 insertions(+)

diff --git a/Documentation/virt/kvm/devices/arm-vgic-v5.rst b/Documentation/virt/kvm/devices/arm-vgic-v5.rst
index 2417eba01830c..46ede907f2b32 100644
--- a/Documentation/virt/kvm/devices/arm-vgic-v5.rst
+++ b/Documentation/virt/kvm/devices/arm-vgic-v5.rst
@@ -64,3 +64,69 @@ Groups:
     -EFAULT  Invalid guest ram access
     -EBUSY   One or more VCPUS are running
     =======  ========================================================
+
+  KVM_DEV_ARM_VGIC_GRP_CPU_SYSREGS
+   Attributes:
+
+    The attr field of kvm_device_attr encodes two values::
+
+      bits:     | 63      ....       32 | 31  ....  16 | 15  ....  0 |
+      values:   |         mpidr         |      RES     |    instr    |
+
+    The mpidr field encodes the CPU ID based on the affinity information in the
+    architecture defined MPIDR, and the field is encoded as follows::
+
+      | 63 .... 56 | 55 .... 48 | 47 .... 40 | 39 .... 32 |
+      |    Aff3    |    Aff2    |    Aff1    |    Aff0    |
+
+    The instr field encodes the system register to access based on the fields
+    defined in the A64 instruction set encoding for system register access
+    (RES means the bits are reserved for future use and should be zero)::
+
+      | 15 ... 14 | 13 ... 11 | 10 ... 7 | 6 ... 3 | 2 ... 0 |
+      |   Op 0    |    Op1    |    CRn   |   CRm   |   Op2   |
+
+    All system regs accessed through this API are (rw, 64-bit) and
+    kvm_device_attr.addr points to a __u64 value.
+
+    KVM_DEV_ARM_VGIC_GRP_CPU_SYSREGS accesses the CPU interface registers for the
+    CPU specified by the mpidr field.
+
+    The available registers are:
+
+    ======================  ====================================================
+    ICC_ICSR_EL1
+    ICC_PPI_ENABLER0_EL1
+    ICC_PPI_ENABLER1_EL1
+    ICC_PPI_SACTIVER0_EL1   ICC_PPI_CACTIVER0_EL1 is not supported. Writes to
+                            ICC_PPI_SACTIVER0_EL1 are treated as RAW writes of
+			    the underlying state.
+    ICC_PPI_SACTIVER1_EL1   ICC_PPI_CACTIVER1_EL1 is not supported. Writes to
+                            ICC_PPI_SACTIVER1_EL1 are treated as RAW writes of
+			    the underlying state.
+    ICC_PPI_SPENDR0_EL1     ICC_PPI_CPENDR0_EL1 is not supported. Writes to
+                            ICC_PPI_SPENDR0_EL1 are treated as RAW writes of
+			    the underlying state.
+    ICC_PPI_SPENDR1_EL1     ICC_PPI_CPENDR1_EL1 is not supported. Writes to
+                            ICC_PPI_SPENDR1_EL1 are treated as RAW writes of
+			    the underlying state.
+    ICC_PPI_PRIORITYR0_EL1
+    ICC_PPI_PRIORITYR1_EL1
+    ICC_PPI_PRIORITYR2_EL1
+    ICC_PPI_PRIORITYR3_EL1
+    ICC_PPI_PRIORITYR4_EL1
+    ICC_PPI_PRIORITYR5_EL1
+    ICC_PPI_PRIORITYR6_EL1
+    ICC_PPI_PRIORITYR7_EL1
+    ICC_PPI_PRIORITYR8_EL1
+    ICC_PPI_PRIORITYR9_EL1
+    ICC_PPI_PRIORITYR10_EL1
+    ICC_PPI_PRIORITYR11_EL1
+    ICC_PPI_PRIORITYR12_EL1
+    ICC_PPI_PRIORITYR13_EL1
+    ICC_PPI_PRIORITYR14_EL1
+    ICC_PPI_PRIORITYR15_EL1
+    ICC_APR_EL1
+    ICC_CR0_EL1
+    ICC_PCR_EL1
+    =======================  ===================================================
-- 
2.34.1