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

Demi Marie Obenour
2025-10-24T22:53:01Z

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On 10/24/25 10:51, 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
>
> If it's easy, why not. But other people should not suffer for all the
> XEN hacks we keep dragging along.

Which hacks? Serious question. Is this just for Xen PV or is HVM
also affected?
--
Sincerely,
Demi Marie Obenour (she/her/hers)

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