diff options
| author | Andrew Jones <drjones@redhat.com> | 2020-01-30 16:02:06 +0000 |
|---|---|---|
| committer | Peter Maydell <peter.maydell@linaro.org> | 2020-01-30 16:02:06 +0000 |
| commit | dea101a1ae9968c9fec6ab0291489dad7c49f36f (patch) | |
| tree | a7c20f44a7f47478a8b475fb42609af5d2977f64 /docs/arm-cpu-features.rst | |
| parent | e5ac4200b4cddf44df9adbef677af0d1f1c579c6 (diff) | |
target/arm/cpu: Add the kvm-no-adjvtime CPU property
kvm-no-adjvtime is a KVM specific CPU property and a first of its
kind. To accommodate it we also add kvm_arm_add_vcpu_properties()
and a KVM specific CPU properties description to the CPU features
document.
Signed-off-by: Andrew Jones <drjones@redhat.com>
Message-id: 20200120101023.16030-7-drjones@redhat.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Diffstat (limited to 'docs/arm-cpu-features.rst')
| -rw-r--r-- | docs/arm-cpu-features.rst | 37 |
1 files changed, 36 insertions, 1 deletions
diff --git a/docs/arm-cpu-features.rst b/docs/arm-cpu-features.rst index 9b537a75e6..dbf3b7cf42 100644 --- a/docs/arm-cpu-features.rst +++ b/docs/arm-cpu-features.rst @@ -31,7 +31,9 @@ supporting the feature or only supporting the feature under certain configurations. For example, the `aarch64` CPU feature, which, when disabled, enables the optional AArch32 CPU feature, is only supported when using the KVM accelerator and when running on a host CPU type that -supports the feature. +supports the feature. While `aarch64` currently only works with KVM, +it could work with TCG. CPU features that are specific to KVM are +prefixed with "kvm-" and are described in "KVM VCPU Features". CPU Feature Probing =================== @@ -171,6 +173,39 @@ disabling many SVE vector lengths would be quite verbose, the `sve<N>` CPU properties have special semantics (see "SVE CPU Property Parsing Semantics"). +KVM VCPU Features +================= + +KVM VCPU features are CPU features that are specific to KVM, such as +paravirt features or features that enable CPU virtualization extensions. +The features' CPU properties are only available when KVM is enabled and +are named with the prefix "kvm-". KVM VCPU features may be probed, +enabled, and disabled in the same way as other CPU features. Below is +the list of KVM VCPU features and their descriptions. + + kvm-no-adjvtime By default kvm-no-adjvtime is disabled. This + means that by default the virtual time + adjustment is enabled (vtime is *not not* + adjusted). + + When virtual time adjustment is enabled each + time the VM transitions back to running state + the VCPU's virtual counter is updated to ensure + stopped time is not counted. This avoids time + jumps surprising guest OSes and applications, + as long as they use the virtual counter for + timekeeping. However it has the side effect of + the virtual and physical counters diverging. + All timekeeping based on the virtual counter + will appear to lag behind any timekeeping that + does not subtract VM stopped time. The guest + may resynchronize its virtual counter with + other time sources as needed. + + Enable kvm-no-adjvtime to disable virtual time + adjustment, also restoring the legacy (pre-5.0) + behavior. + SVE CPU Properties ================== |