[PATCH v4 25/25] KVM: arm64/sve: Document KVM API extensions for SVE

[Dave Martin <Dave.Martin@arm.com>]

This patch adds sections to the KVM API documentation describing
the extensions for supporting the Scalable Vector Extension (SVE)
in guests.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>

---

Changes since RFC v3:

 * Rewrote the bulk of the documentation to document the new vector
   length set control interface via KVM_REG_ARM64_SVE_VLS, and describe
   the new vcpu init / register access semantics.

 * Fix documentation regarding which SVE Zn register bits must be
   accessed in order to get at Vn on an SVE-enabled vcpu.
---
 Documentation/virtual/kvm/api.txt | 61 +++++++++++++++++++++++++++++++++++++--
 1 file changed, 58 insertions(+), 3 deletions(-)

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index cb15f2a..d45e93c 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1856,6 +1856,7 @@ Parameters: struct kvm_one_reg (in)
 Returns: 0 on success, negative value on failure
 Errors:
   ENOENT:   no such register
+  EPERM:    register access forbidden for architecture-dependent reasons
   EINVAL:   other errors, such as bad size encoding for a known register
 
 struct kvm_one_reg {
@@ -2110,13 +2111,20 @@ Specifically:
   0x6030 0000 0010 004c SPSR_UND    64  spsr[KVM_SPSR_UND]
   0x6030 0000 0010 004e SPSR_IRQ    64  spsr[KVM_SPSR_IRQ]
   0x6060 0000 0010 0050 SPSR_FIQ    64  spsr[KVM_SPSR_FIQ]
-  0x6040 0000 0010 0054 V0         128  fp_regs.vregs[0]
-  0x6040 0000 0010 0058 V1         128  fp_regs.vregs[1]
+  0x6040 0000 0010 0054 V0         128  fp_regs.vregs[0]    (*)
+  0x6040 0000 0010 0058 V1         128  fp_regs.vregs[1]    (*)
     ...
-  0x6040 0000 0010 00d0 V31        128  fp_regs.vregs[31]
+  0x6040 0000 0010 00d0 V31        128  fp_regs.vregs[31]   (*)
   0x6020 0000 0010 00d4 FPSR        32  fp_regs.fpsr
   0x6020 0000 0010 00d5 FPCR        32  fp_regs.fpcr
 
+(*) These encodings are not accepted for SVE-enabled vcpus.  See
+    KVM_ARM_VCPU_INIT.
+
+    The equivalent register content can be accessed via bits [127:0] of
+    the corresponding SVE Zn registers instead for vcpus that have SVE
+    enabled (see below).
+
 arm64 CCSIDR registers are demultiplexed by CSSELR value:
   0x6020 0000 0011 00 <csselr:8>
 
@@ -2126,6 +2134,50 @@ arm64 system registers have the following id bit patterns:
 arm64 firmware pseudo-registers have the following bit pattern:
   0x6030 0000 0014 <regno:16>
 
+arm64 SVE registers have the following bit patterns:
+  0x6080 0000 0015 00 <n:5> <slice:5>   Zn bits[2048*slice + 2047 : 2048*slice]
+  0x6050 0000 0015 04 <n:4> <slice:5>   Pn bits[256*slice + 255 : 256*slice]
+  0x6050 0000 0015 060 <slice:5>        FFR bits[256*slice + 255 : 256*slice]
+  0x6060 0000 0015 ffff                 KVM_REG_ARM64_SVE_VLS pseudo-register
+
+These registers are only accessible on vcpus for which SVE is enabled.
+See KVM_ARM_VCPU_INIT for details.
+
+KVM_REG_ARM64_SVE_VLS is a pseudo-register that allows the set of vector
+lengths supported by the vcpu to be discovered and configured by
+userspace.  When transferred to or from user memory via KVM_GET_ONE_REG
+or KVM_SET_ONE_REG, the value of this register is of type __u64[8], and
+encodes the set of vector lengths as follows:
+
+__u64 vector_lengths[8];
+
+if (vq >= SVE_VQ_MIN && vq <= SVE_VQ_MAX &&
+    ((vector_lengths[(vq - 1) / 64] >> ((vq - 1) % 64)) & 1))
+	/* Vector length vq * 16 bytes supported */
+else
+	/* Vector length vq * 16 bytes not supported */
+
+(See Documentation/arm64/sve.txt for an explanation of the "vq"
+nomenclature.)
+
+KVM_REG_ARM64_SVE_VLS is only accessible after KVM_ARM_VCPU_INIT.
+KVM_ARM_VCPU_INIT initialises it to the best set of vector lengths that
+the host supports.
+
+Userspace may subsequently modify it if desired until the vcpu
+configuration is finalized by accessing the guest's SVE registers, or
+enumerating them via KVM_GET_REG_LIST, or setting the cpu running via
+KVM_RUN.
+
+Apart from simply removing all vector lengths from the host set that
+exceed some value, support for arbitrarily chosen sets of vector lengths
+is hardware-dependent and may not be available.  Attempting to configure
+an invalid set of vector lengths via KVM_SET_ONE_REG will fail with
+EINVAL.
+
+After the vcpu's configuration is finalized, further attempts to write
+this register will fail with EPERM.
+
 
 MIPS registers are mapped using the lower 32 bits.  The upper 16 of that is
 the register group type:
@@ -2180,6 +2232,7 @@ Parameters: struct kvm_one_reg (in and out)
 Returns: 0 on success, negative value on failure
 Errors:
   ENOENT:   no such register
+  EPERM:    register access forbidden for architecture-dependent reasons
   EINVAL:   other errors, such as bad size encoding for a known register
 
 This ioctl allows to receive the value of a single register implemented
@@ -2672,6 +2725,8 @@ Possible features:
 	  Depends on KVM_CAP_ARM_PSCI_0_2.
 	- KVM_ARM_VCPU_PMU_V3: Emulate PMUv3 for the CPU.
 	  Depends on KVM_CAP_ARM_PMU_V3.
+	- KVM_ARM_VCPU_SVE: Enables SVE for the CPU (arm64 only).
+	  Depends on KVM_CAP_ARM_SVE.
 
 
 4.83 KVM_ARM_PREFERRED_TARGET
-- 
2.1.4


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel