linux-kernel - Re: [stable][PATCH] PCIe hot-plug for Intel IOMMU

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Message-ID: <1259389057.3691.2186.camel@macbook.infradead.org>
Date:	Sat, 28 Nov 2009 06:17:37 +0000
From:	David Woodhouse <dwmw2@...radead.org>
To:	Yinghai Lu <yhlu.kernel@...il.com>
Cc:	Fenghua Yu <fenghua.yu@...el.com>,
	"Barnes, Jesse" <jesse.barnes@...el.com>, Greg KH <gregkh@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	torvalds@...ux-foundation.org, jbarnes@...tuousgeek.org,
	stable@...nel.org, iommu@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [stable][PATCH] PCIe hot-plug for Intel IOMMU

On Wed, 2009-11-11 at 13:27 -0800, Yinghai Lu wrote:
> On Wed, Nov 11, 2009 at 7:23 AM, Fenghua Yu <fenghua.yu@...el.com> wrote:
> > To support PCIe hot plug in IOMMU, we register a notifier to respond to device
> > change action.
> >
> > When the notifier gets BUS_NOTIFY_UNBOUND_DRIVER, it removes the device from its
> > DMAR domain.
> >
> > A hot added device will be added into an IOMMU domain when it first does IOMMU
> > op. So there is no need to add more code for hot add.
> >
> > Without the patch, after a hot-remove, a hot-added device on the same slot will
> > not work.
> >
> > Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> 
> Tested-by: Yinghai Lu <yinghai@...nel.org>

But not with 'intel_iommu=igfx_off', I note. The call to find_domain()
will oops when it runs on the graphics device with ->archdata.iommu ==
DUMMY_DEVICE_DOMAIN_INFO (== -1). All other calls to find_domain() are
guaranteed not to happen for such devices.

One might argue that find_domain() should cope, but do we really want to
be doing that extra check in the unmap fast path?

Testing this fix now...

diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
index 1840a05..f44a015 100644
--- a/drivers/pci/intel-iommu.c
+++ b/drivers/pci/intel-iommu.c
@@ -3228,6 +3228,9 @@ static int device_notifier(struct notifier_block *nb,
 	struct pci_dev *pdev = to_pci_dev(dev);
 	struct dmar_domain *domain;
 
+	if (iommu_no_mapping(dev))
+		return 0;
+
 	domain = find_domain(pdev);
 	if (!domain)
 		return 0;


-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@...el.com                              Intel Corporation

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