On 24/10/2025 17:17, David Woodhouse wrote:

On Fri, 2025-10-24 at 17:05 +0200, Kevin Brodsky wrote:

quoted

On 24/10/2025 16:47, David Woodhouse wrote:

quoted

On Thu, 2025-10-23 at 22:06 +0200, David Hildenbrand wrote:

quoted

On 15.10.25 10:27, Kevin Brodsky wrote:

quoted

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 <redacted>
---

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?

I considered boot-testing a Xen guest (considering the Xen-specific
changes in this series), but having no idea how to go about it I quickly
gave up... Happy to follow instructions :)

https://qemu-project.gitlab.io/qemu/system/i386/xen.html covers booting
Xen HVM guests, and near the bottom PV guests too (for which you do
need a copy of Xen to run in QEMU with '--kernel xen', and your
distro's build should suffice for that).

Let me know if you have any trouble. Here's a sample command line which
works here...

qemu-system-x86_64 -display none --accel kvm,xen-version=0x40011,kernel-irqchip=split -drive file=/var/lib/libvirt/images/fedora28.qcow2,if=xen -kernel ~/git/linux-2.6/arch/x86/boot/bzImage -append "root=/dev/xvda1 console=ttyS0" -serial mon:stdio

Thanks this is helpful! Unfortunately lazy_mmu is only used in the PV
case, so I'd need to run a PV guest. And the distro I'm using (Arch
Linux) does not have a Xen package :/ It can be built from source from
the AUR but that looks rather involved. Are there some prebuilt binaries
I could grab and just point QEMU to?

- Kevin