[PATCH 2/7] iommu: add api to get iommu_domain of a device

[Bhushan Bharat-R65777]

> -----Original Message-----
> From: Bhushan Bharat-R65777
> Sent: Friday, October 04, 2013 3:24 PM
> To: 'Alex Williamson'
> Cc: joro at 8bytes.org; benh at kernel.crashing.org; galak at kernel.crashing.org; linux-
> kernel at vger.kernel.org; linuxppc-dev at lists.ozlabs.org; linux-
> pci at vger.kernel.org; agraf at suse.de; Wood Scott-B07421; iommu at lists.linux-
> foundation.org
> Subject: RE: [PATCH 2/7] iommu: add api to get iommu_domain of a device
> 
> 
> 
> > -----Original Message-----
> > From: linux-pci-owner at vger.kernel.org
> > [mailto:linux-pci-owner at vger.kernel.org]
> > On Behalf Of Alex Williamson
> > Sent: Wednesday, September 25, 2013 10:16 PM
> > To: Bhushan Bharat-R65777
> > Cc: joro at 8bytes.org; benh at kernel.crashing.org;
> > galak at kernel.crashing.org; linux- kernel at vger.kernel.org;
> > linuxppc-dev at lists.ozlabs.org; linux- pci at vger.kernel.org;
> > agraf at suse.de; Wood Scott-B07421; iommu at lists.linux- foundation.org;
> > Bhushan Bharat-R65777
> > Subject: Re: [PATCH 2/7] iommu: add api to get iommu_domain of a
> > device
> >
> > On Thu, 2013-09-19 at 12:59 +0530, Bharat Bhushan wrote:
> > > This api return the iommu domain to which the device is attached.
> > > The iommu_domain is required for making API calls related to iommu.
> > > Follow up patches which use this API to know iommu maping.
> > >
> > > Signed-off-by: Bharat Bhushan <bharat.bhushan at freescale.com>
> > > ---
> > >  drivers/iommu/iommu.c |   10 ++++++++++
> > >  include/linux/iommu.h |    7 +++++++
> > >  2 files changed, 17 insertions(+), 0 deletions(-)
> > >
> > > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c index
> > > fbe9ca7..6ac5f50 100644
> > > --- a/drivers/iommu/iommu.c
> > > +++ b/drivers/iommu/iommu.c
> > > @@ -696,6 +696,16 @@ void iommu_detach_device(struct iommu_domain
> > > *domain, struct device *dev)  }
> > > EXPORT_SYMBOL_GPL(iommu_detach_device);
> > >
> > > +struct iommu_domain *iommu_get_dev_domain(struct device *dev) {
> > > +	struct iommu_ops *ops = dev->bus->iommu_ops;
> > > +
> > > +	if (unlikely(ops == NULL || ops->get_dev_iommu_domain == NULL))
> > > +		return NULL;
> > > +
> > > +	return ops->get_dev_iommu_domain(dev); }
> > > +EXPORT_SYMBOL_GPL(iommu_get_dev_domain);
> >
> > What prevents this from racing iommu_domain_free()?  There's no
> > references acquired, so there's no reason for the caller to assume the pointer
> is valid.
> 
> Sorry for late query, somehow this email went into a folder and escaped;
> 
> Just to be sure, there is not lock at generic "struct iommu_domain", but IP
> specific structure (link FSL domain) linked in iommu_domain->priv have a lock,
> so we need to ensure this race in FSL iommu code (say
> drivers/iommu/fsl_pamu_domain.c), right?

Further thinking of this, there are more problems here:
 - Like MSI subsystem will call iommu_get_dev_domain(), which will take a lock, find the domain pointer, release the lock, and return the domain
 - Now if domain in freed up
 - While MSI subsystem tries to do work on domain (like get_attribute/set_attribute etc) ???

So can we do like iommu_get_dev_domain() will return domain with the lock held, and iommu_put_dev_domain() will release the lock? And iommu_get_dev_domain() must always be followed by iommu_get_dev_domain()

Thanks
-Bharat

> 
> Thanks
> -Bharat
> 
> >
> > >  /*
> > >   * IOMMU groups are really the natrual working unit of the IOMMU, but
> > >   * the IOMMU API works on domains and devices.  Bridge that gap by
> > > diff --git a/include/linux/iommu.h b/include/linux/iommu.h index
> > > 7ea319e..fa046bd 100644
> > > --- a/include/linux/iommu.h
> > > +++ b/include/linux/iommu.h
> > > @@ -127,6 +127,7 @@ struct iommu_ops {
> > >  	int (*domain_set_windows)(struct iommu_domain *domain, u32 w_count);
> > >  	/* Get the numer of window per domain */
> > >  	u32 (*domain_get_windows)(struct iommu_domain *domain);
> > > +	struct iommu_domain *(*get_dev_iommu_domain)(struct device *dev);
> > >
> > >  	unsigned long pgsize_bitmap;
> > >  };
> > > @@ -190,6 +191,7 @@ extern int iommu_domain_window_enable(struct
> > > iommu_domain
> > *domain, u32 wnd_nr,
> > >  				      phys_addr_t offset, u64 size,
> > >  				      int prot);
> > >  extern void iommu_domain_window_disable(struct iommu_domain
> > > *domain,
> > > u32 wnd_nr);
> > > +extern struct iommu_domain *iommu_get_dev_domain(struct device
> > > +*dev);
> > >  /**
> > >   * report_iommu_fault() - report about an IOMMU fault to the IOMMU
> framework
> > >   * @domain: the iommu domain where the fault has happened @@ -284,6
> > > +286,11 @@ static inline void iommu_domain_window_disable(struct
> > > iommu_domain *domain,  {  }
> > >
> > > +static inline struct iommu_domain *iommu_get_dev_domain(struct
> > > +device
> > > +*dev) {
> > > +	return NULL;
> > > +}
> > > +
> > >  static inline phys_addr_t iommu_iova_to_phys(struct iommu_domain
> > > *domain, dma_addr_t iova)  {
> > >  	return 0;
> >
> >
> >
> > --
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