Re: [PATCH v5 04/12] iommu/sva: Basic data structures for SVA

[Baolu Lu <baolu.lu@linux.intel.com>]

On 2022/5/4 02:09, Jean-Philippe Brucker wrote:
> On Mon, May 02, 2022 at 09:48:34AM +0800, Lu Baolu wrote:
>> Use below data structures for SVA implementation in the IOMMU core:
>>
>> - struct iommu_sva_ioas
>>    Represent the I/O address space shared with an application CPU address
>>    space. This structure has a 1:1 relationship with an mm_struct. It
>>    grabs a "mm->mm_count" refcount during creation and drop it on release.
> 
> Do we actually need this structure?  At the moment it only keeps track of
> bonds, which we can move to struct dev_iommu. Replacing it by a mm pointer
> in struct iommu_domain simplifies the driver and seems to work

Fair enough.

+struct iommu_sva_ioas {
+	struct mm_struct *mm;
+	ioasid_t pasid;
+
+	/* Counter of domains attached to this ioas. */
+	refcount_t users;
+
+	/* All bindings are linked here. */
+	struct list_head bonds;
+};

By moving @mm to struct iommu_domain and @bonds to struct dev_iommu, the
code looks simpler. The mm, sva domain and per-device dev_iommu are
guaranteed to be valid during bind() and unbind().

Will head this direction in the next version.

> 
> Thanks,
> Jean

Best regards,
baolu

> 
>>
>> - struct iommu_domain (IOMMU_DOMAIN_SVA type)
>>    Represent a hardware pagetable that the IOMMU hardware could use for
>>    SVA translation. Multiple iommu domains could be bound with an SVA ioas
>>    and each grabs a refcount from ioas in order to make sure ioas could
>>    only be freed after all domains have been unbound.
>>
>> - struct iommu_sva
>>    Represent a bond relationship between an SVA ioas and an iommu domain.
>>    If a bond already exists, it's reused and a reference is taken.
>>
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>> ---
>>   include/linux/iommu.h         | 14 +++++++++++++-
>>   drivers/iommu/iommu-sva-lib.h |  1 +
>>   drivers/iommu/iommu-sva-lib.c | 18 ++++++++++++++++++
>>   3 files changed, 32 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>> index ab36244d4e94..f582f434c513 100644
>> --- a/include/linux/iommu.h
>> +++ b/include/linux/iommu.h
>> @@ -42,6 +42,7 @@ struct notifier_block;
>>   struct iommu_sva;
>>   struct iommu_fault_event;
>>   struct iommu_dma_cookie;
>> +struct iommu_sva_ioas;
>>   
>>   /* iommu fault flags */
>>   #define IOMMU_FAULT_READ	0x0
>> @@ -64,6 +65,9 @@ struct iommu_domain_geometry {
>>   #define __IOMMU_DOMAIN_PT	(1U << 2)  /* Domain is identity mapped   */
>>   #define __IOMMU_DOMAIN_DMA_FQ	(1U << 3)  /* DMA-API uses flush queue    */
>>   
>> +#define __IOMMU_DOMAIN_SHARED	(1U << 4)  /* Page table shared from CPU  */
>> +#define __IOMMU_DOMAIN_HOST_VA	(1U << 5)  /* Host CPU virtual address */
>> +
>>   /*
>>    * This are the possible domain-types
>>    *
>> @@ -86,6 +90,8 @@ struct iommu_domain_geometry {
>>   #define IOMMU_DOMAIN_DMA_FQ	(__IOMMU_DOMAIN_PAGING |	\
>>   				 __IOMMU_DOMAIN_DMA_API |	\
>>   				 __IOMMU_DOMAIN_DMA_FQ)
>> +#define IOMMU_DOMAIN_SVA	(__IOMMU_DOMAIN_SHARED |	\
>> +				 __IOMMU_DOMAIN_HOST_VA)
>>   
>>   struct iommu_domain {
>>   	unsigned type;
>> @@ -95,6 +101,7 @@ struct iommu_domain {
>>   	void *handler_token;
>>   	struct iommu_domain_geometry geometry;
>>   	struct iommu_dma_cookie *iova_cookie;
>> +	struct iommu_sva_ioas *sva_ioas;
>>   };
>>   
>>   static inline bool iommu_is_dma_domain(struct iommu_domain *domain)
>> @@ -628,7 +635,12 @@ struct iommu_fwspec {
>>    * struct iommu_sva - handle to a device-mm bond
>>    */
>>   struct iommu_sva {
>> -	struct device			*dev;
>> +	struct device		*dev;
>> +	struct iommu_sva_ioas	*sva_ioas;
>> +	struct iommu_domain	*domain;
>> +	/* Link to sva ioas's bonds list */
>> +	struct list_head	node;
>> +	refcount_t		users;
>>   };
>>   
>>   int iommu_fwspec_init(struct device *dev, struct fwnode_handle *iommu_fwnode,
>> diff --git a/drivers/iommu/iommu-sva-lib.h b/drivers/iommu/iommu-sva-lib.h
>> index 8909ea1094e3..9c5e108e2c8a 100644
>> --- a/drivers/iommu/iommu-sva-lib.h
>> +++ b/drivers/iommu/iommu-sva-lib.h
>> @@ -10,6 +10,7 @@
>>   
>>   int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t max);
>>   struct mm_struct *iommu_sva_find(ioasid_t pasid);
>> +struct mm_struct *iommu_sva_domain_mm(struct iommu_domain *domain);
>>   
>>   /* I/O Page fault */
>>   struct device;
>> diff --git a/drivers/iommu/iommu-sva-lib.c b/drivers/iommu/iommu-sva-lib.c
>> index 106506143896..d524a402be3b 100644
>> --- a/drivers/iommu/iommu-sva-lib.c
>> +++ b/drivers/iommu/iommu-sva-lib.c
>> @@ -3,6 +3,8 @@
>>    * Helpers for IOMMU drivers implementing SVA
>>    */
>>   #include <linux/mutex.h>
>> +#include <linux/iommu.h>
>> +#include <linux/slab.h>
>>   #include <linux/sched/mm.h>
>>   
>>   #include "iommu-sva-lib.h"
>> @@ -10,6 +12,22 @@
>>   static DEFINE_MUTEX(iommu_sva_lock);
>>   static DECLARE_IOASID_SET(iommu_sva_pasid);
>>   
>> +struct iommu_sva_ioas {
>> +	struct mm_struct *mm;
>> +	ioasid_t pasid;
>> +
>> +	/* Counter of domains attached to this ioas. */
>> +	refcount_t users;
>> +
>> +	/* All bindings are linked here. */
>> +	struct list_head bonds;
>> +};
>> +
>> +struct mm_struct *iommu_sva_domain_mm(struct iommu_domain *domain)
>> +{
>> +	return domain->sva_ioas->mm;
>> +}
>> +
>>   /**
>>    * iommu_sva_alloc_pasid - Allocate a PASID for the mm
>>    * @mm: the mm
>> -- 
>> 2.25.1
>>

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