Re: [PATCH v2 2/2] x86/xen: Allow per-domain usage of hardware virtualized APIC

[Jane Malalane <Jane.Malalane@citrix.com>]

On 10/02/2022 10:09, Roger Pau Monné wrote:
> On Mon, Feb 07, 2022 at 06:21:01PM +0000, 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 vitualization, 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 running APIC
>> read/write accesses without taking a VM exit.
>>
>> Being able to disable x{2}APIC hardware assisted vitualization can be
>> useful for testing and debugging purposes.
> 
> Might be worth adding a note to the commit log in order to note that
> vmx_install_vlapic_mapping doesn't require modifications regardless of
> whether the guest has virtualize_apic_accesses enabled or not.
> 
> Setting the APIC_ACCESS_ADDR VMCS field is fine even if
> virtualize_apic_accesses is not enabled for the guest: as long as the
> feature is supported by the CPU the field will exist.
Oh right. Will add these two points.

Thanks,

Jane.