On Fri, Apr 01, 2022 at 11:47:13AM +0100, Jane Malalane wrote:
> 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 configuration file,
> so it is safe to migrate a guest that doesn't have assisted_x{2}apic
> set in its config file between hosts that have different support for
> hardware assisted x{2}APIC virtualization.
>
> Suggested-by: Andrew Cooper <andrew.coop...@citrix.com>
> Signed-off-by: Jane Malalane <jane.malal...@citrix.com>
Reviewed-by: Roger Pau Monné <roger....@citrix.com>
Thanks, Roger.
