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Re: [RFC PATCH for-4.22] x86/hvm: Introduce force_x2apic flag
- To: Jan Beulich <jbeulich@xxxxxxxx>, Grygorii Strashko <grygorii_strashko@xxxxxxxx>
- From: Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>
- Date: Tue, 11 Nov 2025 13:36:07 +0100
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- Cc: Anthony PERARD <anthony.perard@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, "Alejandro.GarciaVallejo@xxxxxxx" <Alejandro.GarciaVallejo@xxxxxxx>, Jason Andryuk <Jason.Andryuk@xxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 11 Nov 2025 12:36:24 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Thu Oct 30, 2025 at 8:46 AM CET, Jan Beulich wrote:
> On 30.10.2025 00:08, Grygorii Strashko wrote:
>> On 29.10.25 20:26, Teddy Astie wrote:
>>> --- a/xen/arch/x86/include/asm/domain.h
>>> +++ b/xen/arch/x86/include/asm/domain.h
>>> @@ -509,6 +509,8 @@ struct arch_domain
>>> #define has_pirq(d) (!!((d)->arch.emulation_flags &
>>> X86_EMU_USE_PIRQ))
>>> #define has_vpci(d) (!!((d)->arch.emulation_flags & X86_EMU_VPCI))
>>>
>>> +#define has_force_x2apic(d) ((d)->arch.hvm.force_x2apic)
>>
>> Would it be possible for you to consider having Kconfig option to make
>> such configuration global, static?
>
> Especially considering the post-commit-message remarks I don't think this can
> be
> other than a per-guest setting.
>
> Jan
It'd certainly be of use to us to compile out the entirety of xAPIC emulation
in favour of x2APIC.
Granted, it imposes restrictions on what guests are able to run and how, but
that might be acceptable in the interest of a leaner hypervisor.
It is fairly annoying there's no architectural means to signal it.
Cheers,
Alejandro
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