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

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Message-ID: <8D8B600C3EC1B64FAD4503F0B66C61F23BB95B@SHSMSX103.ccr.corp.intel.com>
Date:   Fri, 8 Nov 2019 08:47:19 +0000
From:   "Zeng, Jason" <jason.zeng@...el.com>
To:     David Woodhouse <dwmw2@...radead.org>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "Zeng, Jason" <jason.zeng@...el.com>
Subject: RE: [PATCH] intel-iommu: Turn off translations at shutdown


> -----Original Message-----
> From: David Woodhouse <dwmw2@...radead.org>
> Sent: Friday, November 8, 2019 3:54 PM
> To: Deepa Dinamani <deepa.kernel@...il.com>; joro@...tes.org; linux-
> kernel@...r.kernel.org
> Cc: iommu@...ts.linux-foundation.org; Zeng, Jason <jason.zeng@...el.com>;
> Tian, Kevin <kevin.tian@...el.com>
> 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