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KVM: arm64/sve: Document KVM API extensions for SVE

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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>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
This commit is contained in:
Dave Martin 2018-09-28 14:39:27 +01:00 committed by Marc Zyngier
parent 395f562f2b
commit 50036ad06b
1 changed files with 129 additions and 3 deletions
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132
Documentation/virtual/kvm/api.txt
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@ -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
------------------------