RE: [PATCH] intel-iommu: Turn off translations at shutdown

[Zeng, Jason]

> -----Original Message-----
> From: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
> Sent: Friday, November 8, 2019 3:54 PM
> To: Deepa Dinamani <deepa.kernel@xxxxxxxxx>; joro@xxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx
> Cc: iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; Zeng, Jason <jason.zeng@xxxxxxxxx>;
> Tian, Kevin <kevin.tian@xxxxxxxxx>
> Subject: Re: [PATCH] intel-iommu: Turn off translations at shutdown
> 
> On Thu, 2019-11-07 at 12:59 -0800, Deepa Dinamani wrote:
> > The intel-iommu driver assumes that the iommu state is
> > cleaned up at the start of the new kernel.
> > But, when we try to kexec boot something other than the
> > Linux kernel, the cleanup cannot be relied upon.
> > Hence, cleanup before we go down for reboot.
> >
> > Keeping the cleanup at initialization also, in case BIOS
> > leaves the IOMMU enabled.
> >
> > I considered turning off iommu only during kexec reboot,
> > but a clean shutdown seems always a good idea. But if
> > someone wants to make it conditional, we can do that.
> 
> This is going to break things for the VMM live update scheme that Jason
> presented at KVM Forum, isn't it?
> 
> In that case we rely on the IOMMU still operating during the
> transition.

For VMM live update case, we should be able to detect and bypass
the shutdown that Deepa introduced here, so keep IOMMU still operating?

Thanks,
Jason