Re: [PATCH v3 11/13] x86/xen: use lazy_mmu_state when context-switching

David Hildenbrand
2025-10-24T15:17:03Z

On 24.10.25 17:13, David Woodhouse wrote:
> On Fri, 2025-10-24 at 16:51 +0200, David Hildenbrand wrote:
>> On 24.10.25 16:47, David Woodhouse wrote:
>>> On Thu, 2025-10-23 at 22:06 +0200, David Hildenbrand wrote:
>>>> On 15.10.25 10:27, Kevin Brodsky wrote:
>>>>> We currently set a TIF flag when scheduling out a task that is in
>>>>> lazy MMU mode, in order to restore it when the task is scheduled
>>>>> again.
>>>>>
>>>>> The generic lazy_mmu layer now tracks whether a task is in lazy MMU
>>>>> mode in task_struct::lazy_mmu_state. We can therefore check that
>>>>> state when switching to the new task, instead of using a separate
>>>>> TIF flag.
>>>>>
>>>>> Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
>>>>> ---
>>>>
>>>>
>>>> Looks ok to me, but I hope we get some confirmation from x86 / xen
>>>> folks.
>>>
>>>
>>> I know tglx has shouted at me in the past for precisely this reminder,
>>> but you know you can test Xen guests under QEMU/KVM now and don't need
>>> to actually run Xen? Has this been boot tested?
>>
>> And after that, boot-testing sparc as well? :D
>
> Also not that hard in QEMU, I believe. Although I do have some SPARC
> boxes in the shed...

Yeah, I once went through the pain of getting a sparc64 system booting
in QEMU with a distro (was it debian?) that was 7 years old or so.

Fantastic experience.

Only took me 2 days IIRC. Absolutely worth it to not break upstream
kernels on a museum piece.

--
Cheers

David / dhildenb