linux-kernel - Re: [PATCH v4 05/16] drivers/iommu: Take a ref to the IOMMU driver prior to ->add

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Date:   Thu, 9 Jan 2020 14:16:03 +0000
From:   Will Deacon <will@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, iommu@...ts.linuxfoundation.org,
        kernel-team@...roid.com,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        John Garry <john.garry@...wei.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Saravana Kannan <saravanak@...gle.com>,
        "Isaac J. Manjarres" <isaacm@...eaurora.org>,
        Robin Murphy <robin.murphy@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Joerg Roedel <joro@...tes.org>,
        Ard Biesheuvel <ardb@...nel.org>
Subject: Re: [PATCH v4 05/16] drivers/iommu: Take a ref to the IOMMU driver
 prior to ->add_device()

Hi Greg,

On Thu, Dec 19, 2019 at 03:44:37PM +0100, Greg Kroah-Hartman wrote:
> On Thu, Dec 19, 2019 at 12:03:41PM +0000, Will Deacon wrote:
> > diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> > index f2223cbb5fd5..e9f94d3f7a04 100644
> > --- a/include/linux/iommu.h
> > +++ b/include/linux/iommu.h
> > @@ -246,9 +246,10 @@ struct iommu_iotlb_gather {
> >   * @sva_get_pasid: Get PASID associated to a SVA handle
> >   * @page_response: handle page request response
> >   * @cache_invalidate: invalidate translation caches
> > - * @pgsize_bitmap: bitmap of all possible supported page sizes
> >   * @sva_bind_gpasid: bind guest pasid and mm
> >   * @sva_unbind_gpasid: unbind guest pasid and mm
> > + * @pgsize_bitmap: bitmap of all possible supported page sizes
> > + * @owner: Driver module providing these ops
> >   */
> >  struct iommu_ops {
> >  	bool (*capable)(enum iommu_cap);
> > @@ -318,6 +319,7 @@ struct iommu_ops {
> >  	int (*sva_unbind_gpasid)(struct device *dev, int pasid);
> >  
> >  	unsigned long pgsize_bitmap;
> > +	struct module *owner;
> 
> Everyone is always going to forget to set this field.  I don't think you
> even set it for all of the different iommu_ops possible in this series,
> right?

I only initialised the field for those drivers which can actually be built
as a module, but I take your point about this being error-prone.

> The "trick" we did to keep people from having to remember this is to do
> what we did for the bus registering functions.
> 
> Look at pci_register_driver in pci.h:
> #define pci_register_driver(driver)             \
>         __pci_register_driver(driver, THIS_MODULE, KBUILD_MODNAME)
> 
> Then we set the .owner field in the "real" __pci_register_driver() call.
> 
> Same thing for USB and lots, if not all, other driver register
> functions.
> 
> You can do the same thing here, and I would recommend it.

Yes, that makes sense, cheers. Diff below. I'll send it to Joerg along
with some other SMMU patches that have come in since the holiday.

Will

--->8

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 03dc97842875..e82997a705a8 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -2733,7 +2733,6 @@ static struct iommu_ops arm_smmu_ops = {
 	.get_resv_regions	= arm_smmu_get_resv_regions,
 	.put_resv_regions	= arm_smmu_put_resv_regions,
 	.pgsize_bitmap		= -1UL, /* Restricted during device attach */
-	.owner			= THIS_MODULE,
 };
 
 /* Probing and initialisation functions */
diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index 5ef1f2e100d7..93d332423f6f 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -1623,7 +1623,6 @@ static struct iommu_ops arm_smmu_ops = {
 	.get_resv_regions	= arm_smmu_get_resv_regions,
 	.put_resv_regions	= arm_smmu_put_resv_regions,
 	.pgsize_bitmap		= -1UL, /* Restricted during device attach */
-	.owner			= THIS_MODULE,
 };
 
 static void arm_smmu_device_reset(struct arm_smmu_device *smmu)
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index e9f94d3f7a04..90007c92ad2d 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -388,12 +388,19 @@ void iommu_device_sysfs_remove(struct iommu_device *iommu);
 int  iommu_device_link(struct iommu_device   *iommu, struct device *link);
 void iommu_device_unlink(struct iommu_device *iommu, struct device *link);
 
-static inline void iommu_device_set_ops(struct iommu_device *iommu,
-					const struct iommu_ops *ops)
+static inline void __iommu_device_set_ops(struct iommu_device *iommu,
+					  const struct iommu_ops *ops)
 {
 	iommu->ops = ops;
 }
 
+#define iommu_device_set_ops(iommu, ops)				\
+do {									\
+	struct iommu_ops *__ops = (struct iommu_ops *)(ops);		\
+	__ops->owner = THIS_MODULE;					\
+	__iommu_device_set_ops(iommu, __ops);				\
+} while (0)
+
 static inline void iommu_device_set_fwnode(struct iommu_device *iommu,
 					   struct fwnode_handle *fwnode)
 {