path: root/docs/arm-cpu-features.rst
diff options
Diffstat (limited to 'docs/arm-cpu-features.rst')
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
+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