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Re: [PATCH v5] x86: make Viridian support optional
- To: Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Grygorii Strashko <grygorii_strashko@xxxxxxxx>
- From: Demi Marie Obenour <demiobenour@xxxxxxxxx>
- Date: Sat, 18 Oct 2025 21:21:37 -0400
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- Cc: Sergiy Kibrik <Sergiy_Kibrik@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Paul Durrant <paul@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Sun, 19 Oct 2025 01:22:28 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 10/17/25 11:52, Alejandro Vallejo wrote:
> On Wed Oct 15, 2025 at 7:58 AM CEST, Demi Marie Obenour wrote:
>> On 10/13/25 06:01, Alejandro Vallejo wrote:
>>> On Wed Oct 8, 2025 at 6:04 PM CEST, Jan Beulich wrote:
>>>> On 30.09.2025 14:52, Grygorii Strashko wrote:
>>>>> --- a/xen/arch/x86/hvm/Kconfig
>>>>> +++ b/xen/arch/x86/hvm/Kconfig
>>>>> @@ -62,6 +62,16 @@ config ALTP2M
>>>>>
>>>>> If unsure, stay with defaults.
>>>>>
>>>>> +config VIRIDIAN
>>>>> + bool "Hyper-V enlightenments for guests" if EXPERT
>>>>> + default y
>>>>> + help
>>>>> + Support optimizations for Hyper-V guests such as faster hypercalls,
>>>>> + efficient timer and interrupt handling, and enhanced paravirtualized
>>>>> + I/O. This is to improve performance and compatibility of Windows VMs.
>>>>
>>>> What is "paravirtualized I/O" about in this context?
>>>
>>> Hypervisor-assisted IPIs, TLB flushes, etc. Or so I understood back when I
>>> said
>>> that looked ok. I see there could be confusion with Xen PV device protocols,
>>> but as far as the user of the help message is concerned it makes no
>>> difference.
>>>
>>> One could even remove the examples and leave it as "... for Hyper-V guests.
>>> This
>>> is to...". They are truly inconsequential.
>>>
>>> All that matters is that (modern) Windows won't run without it, and that it
>>> provides some indeterminate hypervisor-provided assists to try to reduce
>>> some
>>> virtualization overheads.
>>
>> Qubes OS doesn't expose Viridian at all, which is why it wasn't
>> vulnerable to XSA-472. It still runs Windows guests just fine.
>
> Can you run Windows 11?
I haven't tried it, but it is documented as working.
> I don't remember which, but I do know some versions of Windows refuse to boot
> if they determine they are virtualised and don't see the mandatory parts of
> the TLFS.
>
> If 11 works, maybe Windows Server?
Windows Server is more likely.
--
Sincerely,
Demi Marie Obenour (she/her/hers) Attachment:
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