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Diffstat (limited to 'docs/arm-cpu-features.rst')
| -rw-r--r-- | docs/arm-cpu-features.rst | 45 |
1 files changed, 33 insertions, 12 deletions
diff --git a/docs/arm-cpu-features.rst b/docs/arm-cpu-features.rst index 2ea4d6e90c..bed218d446 100644 --- a/docs/arm-cpu-features.rst +++ b/docs/arm-cpu-features.rst @@ -191,10 +191,18 @@ SVE CPU Property Dependencies and Constraints 1) At least one vector length must be enabled when `sve` is enabled. - 2) If a vector length `N` is enabled, then all power-of-two vector - lengths smaller than `N` must also be enabled. E.g. if `sve512` - is enabled, then the 128-bit and 256-bit vector lengths must also - be enabled. + 2) If a vector length `N` is enabled, then, when KVM is enabled, all + smaller, host supported vector lengths must also be enabled. If + KVM is not enabled, then only all the smaller, power-of-two vector + lengths must be enabled. E.g. with KVM if the host supports all + vector lengths up to 512-bits (128, 256, 384, 512), then if `sve512` + is enabled, the 128-bit vector length, 256-bit vector length, and + 384-bit vector length must also be enabled. Without KVM, the 384-bit + vector length would not be required. + + 3) If KVM is enabled then only vector lengths that the host CPU type + support may be enabled. If SVE is not supported by the host, then + no `sve*` properties may be enabled. SVE CPU Property Parsing Semantics ---------------------------------- @@ -209,8 +217,10 @@ SVE CPU Property Parsing Semantics an error is generated. 2) If SVE is enabled (`sve=on`), but no `sve<N>` CPU properties are - provided, then all supported vector lengths are enabled, including - the non-power-of-two lengths. + provided, then all supported vector lengths are enabled, which when + KVM is not in use means including the non-power-of-two lengths, and, + when KVM is in use, it means all vector lengths supported by the host + processor. 3) If SVE is enabled, then an error is generated when attempting to disable the last enabled vector length (see constraint (1) of "SVE @@ -221,20 +231,31 @@ SVE CPU Property Parsing Semantics has been explicitly disabled, then an error is generated (see constraint (2) of "SVE CPU Property Dependencies and Constraints"). - 5) If one or more `sve<N>` CPU properties are set `off`, but no `sve<N>`, + 5) When KVM is enabled, if the host does not support SVE, then an error + is generated when attempting to enable any `sve*` properties (see + constraint (3) of "SVE CPU Property Dependencies and Constraints"). + + 6) When KVM is enabled, if the host does support SVE, then an error is + generated when attempting to enable any vector lengths not supported + by the host (see constraint (3) of "SVE CPU Property Dependencies and + Constraints"). + + 7) If one or more `sve<N>` CPU properties are set `off`, but no `sve<N>`, CPU properties are set `on`, then the specified vector lengths are disabled but the default for any unspecified lengths remains enabled. - Disabling a power-of-two vector length also disables all vector - lengths larger than the power-of-two length (see constraint (2) of - "SVE CPU Property Dependencies and Constraints"). + When KVM is not enabled, disabling a power-of-two vector length also + disables all vector lengths larger than the power-of-two length. + When KVM is enabled, then disabling any supported vector length also + disables all larger vector lengths (see constraint (2) of "SVE CPU + Property Dependencies and Constraints"). - 6) If one or more `sve<N>` CPU properties are set to `on`, then they + 8) If one or more `sve<N>` CPU properties are set to `on`, then they are enabled and all unspecified lengths default to disabled, except for the required lengths per constraint (2) of "SVE CPU Property Dependencies and Constraints", which will even be auto-enabled if they were not explicitly enabled. - 7) If SVE was disabled (`sve=off`), allowing all vector lengths to be + 9) If SVE was disabled (`sve=off`), allowing all vector lengths to be explicitly disabled (i.e. avoiding the error specified in (3) of "SVE CPU Property Parsing Semantics"), then if later an `sve=on` is provided an error will be generated. To avoid this error, one must |