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

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Message-ID: <addba4e401c3bf23b86cf8dff97256282895e29f.camel@infradead.org>
Date:   Fri, 08 Nov 2019 08:57:11 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     "Zeng, Jason" <jason.zeng@...el.com>,
        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>
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@...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?

Is that a 'yes' to Deepa's "if someone wants to make it conditional, we
can do that" ? 


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