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

[Zeng, Jason]

> -----Original Message-----
> From: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
> Sent: Friday, November 8, 2019 4:57 PM
> To: Zeng, Jason <jason.zeng@xxxxxxxxx>; Deepa Dinamani
> <deepa.kernel@xxxxxxxxx>; joro@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Cc: iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; Tian, Kevin <kevin.tian@xxxxxxxxx>
> Subject: Re: [PATCH] intel-iommu: Turn off translations at shutdown
> 
> On Fri, 2019-11-08 at 08:47 +0000, Zeng, Jason wrote:
> > > -----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?
> 
> Is that a 'yes' to Deepa's "if someone wants to make it conditional, we
> can do that" ?

Yes, I think so. Thanks!