[PATCH v7 27/27] KVM: arm64/sve: Document KVM API extensions for SVE

Dave Martin
2019-03-29T13:05:39Z

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 v5:

* Document KVM_ARM_VCPU_FINALIZE and its interactions with SVE.
---
Documentation/virtual/kvm/api.txt | 132 +++++++++++++++++++++++++++++++++++++-
1 file changed, 129 insertions(+), 3 deletions(-)

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index cd920dd..68509de 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1873,6 +1873,7 @@ 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 {
@@ -2127,13 +2128,20 @@ 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>

@@ -2143,6 +2151,61 @@ 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
+
+Access to slices beyond the maximum vector length configured for the
+vcpu (i.e., where 16 * slice >= max_vq (**)) will fail with ENOENT.
+
+These registers are only accessible on vcpus for which SVE is enabled.
+See KVM_ARM_VCPU_INIT for details.
+
+In addition, except for KVM_REG_ARM64_SVE_VLS, these registers are not
+accessible until the vcpu's SVE configuration has been finalized
+using KVM_ARM_VCPU_FINALIZE(KVM_ARM_VCPU_SVE). See KVM_ARM_VCPU_INIT
+and KVM_ARM_VCPU_FINALIZE for more information about this procedure.
+
+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 */
+
+(**) The maximum value vq for which the above condition is true is
+max_vq. This is the maximum vector length available to the guest on
+this vcpu, and determines which register slices are visible through
+this ioctl interface.
+
+(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's SVE
+configuration is finalized using KVM_ARM_VCPU_FINALIZE(KVM_ARM_VCPU_SVE).
+
+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 SVE 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:
@@ -2197,6 +2260,7 @@ 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
@@ -2690,6 +2754,33 @@ Possible features:
- 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.
+ Requires KVM_ARM_VCPU_FINALIZE(KVM_ARM_VCPU_SVE):
+
+ * After KVM_ARM_VCPU_INIT:
+
+ - KVM_REG_ARM64_SVE_VLS may be read using KVM_GET_ONE_REG: the
+ initial value of this pseudo-register indicates the best set of
+ vector lengths possible for a vcpu on this host.
+
+ * Before KVM_ARM_VCPU_FINALIZE(KVM_ARM_VCPU_SVE):
+
+ - KVM_RUN and KVM_GET_REG_LIST are not available;
+
+ - KVM_GET_ONE_REG and KVM_SET_ONE_REG cannot be used to access
+ the scalable archietctural SVE registers
+ KVM_REG_ARM64_SVE_ZREG(), KVM_REG_ARM64_SVE_PREG() or
+ KVM_REG_ARM64_SVE_FFR;
+
+ - KVM_REG_ARM64_SVE_VLS may optionally be written using
+ KVM_SET_ONE_REG, to modify the set of vector lengths available
+ for the vcpu.
+
+ * After KVM_ARM_VCPU_FINALIZE(KVM_ARM_VCPU_SVE):
+
+ - the KVM_REG_ARM64_SVE_VLS pseudo-register is immutable, and can
+ no longer be written using KVM_SET_ONE_REG.

4.83 KVM_ARM_PREFERRED_TARGET

@@ -3904,6 +3995,41 @@ number of valid entries in the 'entries' array, which is then filled.
'index' and 'flags' fields in 'struct kvm_cpuid_entry2' are currently reserved,
userspace should not expect to get any particular value there.

+4.119 KVM_ARM_VCPU_FINALIZE
+
+Capability: KVM_CAP_ARM_SVE
+Architectures: arm, arm64
+Type: vcpu ioctl
+Parameters: int feature (in)
+Returns: 0 on success, -1 on error
+Errors:
+ EPERM: feature not enabled, needs configuration, or already finalized
+ EINVAL: unknown feature
+
+Recognised values for feature:
+ arm64 KVM_ARM_VCPU_SVE
+
+Finalizes the configuration of the specified vcpu feature.
+
+The vcpu must already have been initialised, enabling the affected feature, by
+means of a successful KVM_ARM_VCPU_INIT call with the appropriate flag set in
+features[].
+
+For affected vcpu features, this is a mandatory step that must be performed
+before the vcpu is fully usable.
+
+Between KVM_ARM_VCPU_INIT and KVM_ARM_VCPU_FINALIZE, the feature may be
+configured by use of ioctls such as KVM_SET_ONE_REG. The exact configuration
+that should be performaned and how to do it are feature-dependent.
+
+Other calls that depend on a particular feature being finalized, such as
+KVM_RUN, KVM_GET_REG_LIST, KVM_GET_ONE_REG and KVM_SET_ONE_REG, will fail with
+-EPERM unless the feature has already been finalized by means of a
+KVM_ARM_VCPU_FINALIZE call.
+
+See KVM_ARM_VCPU_INIT for details of vcpu features that require finalization
+using this ioctl.
+
5. The kvm_run structure
------------------------

--
2.1.4