linux-kernel - Re: [PATCH 3/4] iommu/of: Don't call iommu_ops->add

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Message-ID: <20181219143451.GY16835@8bytes.org>
Date:   Wed, 19 Dec 2018 15:34:51 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        jroedel@...e.de, Sudeep Holla <sudeep.holla@....com>,
        Robin Murphy <robin.murphy@....com>,
        Krzysztof Kozlowski <krzk@...nel.org>
Subject: Re: [PATCH 3/4] iommu/of: Don't call iommu_ops->add_device directly

Hi Marek,

thanks for the report!

On Wed, Dec 19, 2018 at 10:54:18AM +0100, Marek Szyprowski wrote:
> On 2018-12-11 16:05, Joerg Roedel wrote:
> > From: Joerg Roedel <jroedel@...e.de>
> >
> > Make sure to invoke this call-back through the proper
> > function of the IOMMU-API.
> >
> > Signed-off-by: Joerg Roedel <jroedel@...e.de>
> > ---
> >  drivers/iommu/of_iommu.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> > index c5dd63072529..4d4847de727e 100644
> > --- a/drivers/iommu/of_iommu.c
> > +++ b/drivers/iommu/of_iommu.c
> > @@ -218,10 +218,10 @@ const struct iommu_ops *of_iommu_configure(struct device *dev,
> >  		ops = dev->iommu_fwspec->ops;
> >  	/*
> >  	 * If we have reason to believe the IOMMU driver missed the initial
> > -	 * add_device callback for dev, replay it to get things in order.
> > +	 * probe for dev, replay it to get things in order.
> >  	 */
> > -	if (ops && ops->add_device && dev->bus && !dev->iommu_group)
> > -		err = ops->add_device(dev);
> > +	if (dev->bus && !dev->iommu_group)
> > +		err = iommu_probe_device(dev);
> 
> This change removes a check for NULL ops, what causes NULL pointer
> exception on first device without IOMMU.

Bummer, this check was supposed to be in iommu_probe_device(), but
apparently it got lost. Does the attached patch fix it?

> I'm also not sure if this is a good idea to call iommu_probe_device(),
> which comes from dev->bus->iommu_ops, which might be different from ops
> from local variable.

The local variable comes from dev->iommu_fwspec->ops, which should be
exactly the same as dev->bus->iommu_ops. I'll leave that for now until
it turns out to be a problem (which I don't expect).


Regards,

	Joerg

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index a2131751dcff..3ed4db334341 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -114,10 +114,14 @@ void iommu_device_unregister(struct iommu_device *iommu)
 int iommu_probe_device(struct device *dev)
 {
 	const struct iommu_ops *ops = dev->bus->iommu_ops;
+	int ret = -EINVAL;
 
 	WARN_ON(dev->iommu_group);
 
-	return ops->add_device(dev);
+	if (ops)
+		ret = ops->add_device(dev);
+
+	return ret;
 }
 
 void iommu_release_device(struct device *dev)