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Diffstat (limited to 'docs/system/arm/cpu-features.rst')
| -rw-r--r-- | docs/system/arm/cpu-features.rst | 76 |
1 files changed, 34 insertions, 42 deletions
diff --git a/docs/system/arm/cpu-features.rst b/docs/system/arm/cpu-features.rst index 00c444042f..f4524b6d3e 100644 --- a/docs/system/arm/cpu-features.rst +++ b/docs/system/arm/cpu-features.rst @@ -177,39 +177,32 @@ 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. - - kvm-steal-time Since v5.2, kvm-steal-time is enabled by - default when KVM is enabled, the feature is - supported, and the guest is 64-bit. - - When kvm-steal-time is enabled a 64-bit guest - can account for time its CPUs were not running - due to the host not scheduling the corresponding - VCPU threads. The accounting statistics may - influence the guest scheduler behavior and/or be - exposed to the guest userspace. +``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. + +``kvm-steal-time`` + Since v5.2, kvm-steal-time is enabled by default when KVM is + enabled, the feature is supported, and the guest is 64-bit. + + When kvm-steal-time is enabled a 64-bit guest can account for time + its CPUs were not running due to the host not scheduling the + corresponding VCPU threads. The accounting statistics may influence + the guest scheduler behavior and/or be exposed to the guest + userspace. TCG VCPU Features ================= @@ -217,16 +210,15 @@ TCG VCPU Features TCG VCPU features are CPU features that are specific to TCG. Below is the list of TCG VCPU features and their descriptions. - pauth-impdef When ``FEAT_Pauth`` is enabled, either the - *impdef* (Implementation Defined) algorithm - is enabled or the *architected* QARMA algorithm - is enabled. By default the impdef algorithm - is disabled, and QARMA is enabled. +``pauth-impdef`` + When ``FEAT_Pauth`` is enabled, either the *impdef* (Implementation + Defined) algorithm is enabled or the *architected* QARMA algorithm + is enabled. By default the impdef algorithm is disabled, and QARMA + is enabled. - The architected QARMA algorithm has good - cryptographic properties, but can be quite slow - to emulate. The impdef algorithm used by QEMU - is non-cryptographic but significantly faster. + The architected QARMA algorithm has good cryptographic properties, + but can be quite slow to emulate. The impdef algorithm used by QEMU + is non-cryptographic but significantly faster. SVE CPU Properties ================== |