[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v9 2/2] x86/xen: Allow per-domain usage of hardware virtualized APIC
On 01.04.2022 12:47, 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. While I can agree this is the case as far as your changes are concerned, it reads as if this was a broader statement. Since hypervisor CPUID leaf contents can change across such a migration (which is pre-existing behavior), I'm not convinced the statement is generally applicable. > Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> > Signed-off-by: Jane Malalane <jane.malalane@xxxxxxxxxx> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx> # hypervisor Jan
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