Introduce a new per-domain creation x86 specific flag to
select whether hardware assisted virtualization should be used for
x{2}APIC.
A per-domain option is added to xl in order to select the usage of
x{2}APIC hardware assisted virtualization, as well as a global
configuration option.
Having all APIC interaction exit to Xen for emulation is slow and can
induce much overhead. Hardware can speed up x{2}APIC by decoding the
APIC access and providing a VM exit with a more specific exit reason
than a regular EPT fault or by altogether avoiding a VM exit.
On the other hand, being able to disable x{2}APIC hardware assisted
virtualization can be useful for testing and debugging purposes.
Note:
- vmx_install_vlapic_mapping doesn't require modifications regardless
of whether the guest has "Virtualize APIC accesses" enabled or not,
i.e., setting the APIC_ACCESS_ADDR VMCS field is fine so long as
virtualize_apic_accesses is supported by the CPU.
- Both per-domain and global assisted_x{2}apic options are not part of
the migration stream, unless explicitly set in the respective
configuration files. Default settings of assisted_x{2}apic done
internally by the toolstack, based on host capabilities at create
time, are not migrated.
Suggested-by: Andrew Cooper <
andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Jane Malalane <
jane.malalane@xxxxxxxxxx>
Reviewed-by: "Roger Pau Monné" <
roger.pau@xxxxxxxxxx>
