RE: [PATCH v1 0/5] target/arm: Handle psci calls in userspace

[Salil Mehta via <qemu-devel@nongnu.org>]

Hi Shaoqin,
Just saw this. Apologies. I missed to reply this earlier as I was bit
disconnected for last few days.


> From: Shaoqin Huang <shahuang@redhat.com>
> Sent: Tuesday, June 27, 2023 3:35 AM

> Hi Salil,
> 
> On 6/26/23 21:42, Salil Mehta wrote:
> >> From: Shaoqin Huang <shahuang@redhat.com>
> >> Sent: Monday, June 26, 2023 7:49 AM
> >> To: qemu-devel@nongnu.org; qemu-arm@nongnu.org
> >> Cc: oliver.upton@linux.dev; Salil Mehta <salil.mehta@huawei.com>;
> >> james.morse@arm.com; gshan@redhat.com; Shaoqin Huang <shahuang@redhat.com>;
> >> Cornelia Huck <cohuck@redhat.com>; kvm@vger.kernel.org; Michael S. Tsirkin
> >> <mst@redhat.com>; Paolo Bonzini <pbonzini@redhat.com>; Peter Maydell <peter.maydell@linaro.org>
> >> Subject: [PATCH v1 0/5] target/arm: Handle psci calls in userspace
> >>
> >> The userspace SMCCC call filtering[1] provides the ability to forward the SMCCC
> >> calls to the userspace. The vCPU hotplug[2] would be the first legitimate use
> >> case to handle the psci calls in userspace, thus the vCPU hotplug can deny the
> >> PSCI_ON call if the vCPU is not present now.
> >>
> >> This series try to enable the userspace SMCCC call filtering, thus can handle
> >> the SMCCC call in userspace. The first enabled SMCCC call is psci call, by using
> >> the new added option 'user-smccc', we can enable handle psci calls in userspace.
> >>
> >> qemu-system-aarch64 -machine virt,user-smccc=on
> >>
> >> This series reuse the qemu implementation of the psci handling, thus the
> >> handling process is very simple. But when handling psci in userspace when using
> >> kvm, the reset vcpu process need to be taking care, the detail is included in
> >> the patch05.
> >
> > This change is intended for VCPU Hotplug and are duplicating the code
> > we are working on. Unless this change is also intended for any other
> > feature I would request you to defer this.
> 
> Thanks for sharing me the information. I'm not intended for merging this
> series, but discuss something about the VCPU Hotplug, since I'm also
> following the work of vCPU Hotplug.

Sure. I am not against this work in any way but there was bit of an overlap and was
trying to avoid that. 

> 
> Just curious, what is your plan to update a new version of VCPU Hotplug
> which is based on the userspace SMCCC filtering?

We have already incorporated this. We have not tested it properly though and
there are some issues related to the migration we are fixing.

I did mention about this in the KVMForum2023 presentation as well.

Latest Qemu Prototype (Pre RFC V2) (Not in the final shape of the patches)
https://github.com/salil-mehta/qemu.git   virt-cpuhp-armv8/rfc-v1-port11052023.dev-1


should work against below kernel changes as confirmed by James,

Latest Kernel Prototype (Pre RFC V2 = RFC V1 + Fixes) 
https://git.gitlab.arm.com/linux-arm/linux-jm.git   virtual_cpu_hotplug/rfc/v2  


We have not added the support of user-configurability which your patch-set does.


Many thanks
Salil.