Re: [PATCH RFC 10/11] iommu: Make IOPF handling framework generic

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

On 2022/3/21 19:39, Jean-Philippe Brucker wrote:
> On Sun, Mar 20, 2022 at 02:40:29PM +0800, Lu Baolu wrote:
>> The existing IOPF handling framework only handles the I/O page faults for
>> SVA. Ginven that we are able to link iommu domain with each I/O page fault,
>> we can now make the I/O page fault handling framework more general for
>> more types of page faults.
>>
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>> ---
>>   include/linux/iommu.h         |  4 +++
>>   drivers/iommu/io-pgfault.c    | 67 ++++++-----------------------------
>>   drivers/iommu/iommu-sva-lib.c | 59 ++++++++++++++++++++++++++++++
>>   3 files changed, 73 insertions(+), 57 deletions(-)
>>
>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>> index 803e7b07605e..11c65a7bed88 100644
>> --- a/include/linux/iommu.h
>> +++ b/include/linux/iommu.h
>> @@ -50,6 +50,8 @@ struct iommu_dma_cookie;
>>   typedef int (*iommu_fault_handler_t)(struct iommu_domain *,
>>   			struct device *, unsigned long, int, void *);
>>   typedef int (*iommu_dev_fault_handler_t)(struct iommu_fault *, void *);
>> +typedef enum iommu_page_response_code (*iommu_domain_iopf_handler_t)
>> +			(struct iommu_fault *, void *);
>>   
>>   struct iommu_domain_geometry {
>>   	dma_addr_t aperture_start; /* First address that can be mapped    */
>> @@ -101,6 +103,8 @@ struct iommu_domain {
>>   	struct iommu_domain_geometry geometry;
>>   	struct iommu_dma_cookie *iova_cookie;
>>   	struct mm_struct *sva_cookie;
>> +	iommu_domain_iopf_handler_t fault_handler;
>> +	void *fault_data;
>>   };
>>   
>>   static inline bool iommu_is_dma_domain(struct iommu_domain *domain)
>> diff --git a/drivers/iommu/io-pgfault.c b/drivers/iommu/io-pgfault.c
>> index 1df8c1dcae77..dad0e40cd8d2 100644
>> --- a/drivers/iommu/io-pgfault.c
>> +++ b/drivers/iommu/io-pgfault.c
>> @@ -69,62 +69,6 @@ static int iopf_complete_group(struct device *dev, struct iopf_fault *iopf,
>>   	return iommu_page_response(dev, &resp);
>>   }
>>   
>> -static enum iommu_page_response_code
>> -iopf_handle_single(struct iopf_fault *iopf)
>> -{
>> -	vm_fault_t ret;
>> -	struct mm_struct *mm;
>> -	struct vm_area_struct *vma;
>> -	unsigned int access_flags = 0;
>> -	unsigned int fault_flags = FAULT_FLAG_REMOTE;
>> -	struct iommu_fault_page_request *prm = &iopf->fault.prm;
>> -	enum iommu_page_response_code status = IOMMU_PAGE_RESP_INVALID;
>> -
>> -	if (!(prm->flags & IOMMU_FAULT_PAGE_REQUEST_PASID_VALID))
>> -		return status;
>> -
>> -	mm = iommu_sva_find(prm->pasid);
>> -	if (IS_ERR_OR_NULL(mm))
>> -		return status;
>> -
>> -	mmap_read_lock(mm);
>> -
>> -	vma = find_extend_vma(mm, prm->addr);
>> -	if (!vma)
>> -		/* Unmapped area */
>> -		goto out_put_mm;
>> -
>> -	if (prm->perm & IOMMU_FAULT_PERM_READ)
>> -		access_flags |= VM_READ;
>> -
>> -	if (prm->perm & IOMMU_FAULT_PERM_WRITE) {
>> -		access_flags |= VM_WRITE;
>> -		fault_flags |= FAULT_FLAG_WRITE;
>> -	}
>> -
>> -	if (prm->perm & IOMMU_FAULT_PERM_EXEC) {
>> -		access_flags |= VM_EXEC;
>> -		fault_flags |= FAULT_FLAG_INSTRUCTION;
>> -	}
>> -
>> -	if (!(prm->perm & IOMMU_FAULT_PERM_PRIV))
>> -		fault_flags |= FAULT_FLAG_USER;
>> -
>> -	if (access_flags & ~vma->vm_flags)
>> -		/* Access fault */
>> -		goto out_put_mm;
>> -
>> -	ret = handle_mm_fault(vma, prm->addr, fault_flags, NULL);
>> -	status = ret & VM_FAULT_ERROR ? IOMMU_PAGE_RESP_INVALID :
>> -		IOMMU_PAGE_RESP_SUCCESS;
>> -
>> -out_put_mm:
>> -	mmap_read_unlock(mm);
>> -	mmput(mm);
>> -
>> -	return status;
>> -}
>> -
>>   static void iopf_handle_group(struct work_struct *work)
>>   {
>>   	struct iopf_group *group;
>> @@ -134,12 +78,21 @@ static void iopf_handle_group(struct work_struct *work)
>>   	group = container_of(work, struct iopf_group, work);
>>   
>>   	list_for_each_entry_safe(iopf, next, &group->faults, list) {
>> +		struct iommu_domain *domain;
>> +
>> +		domain = iommu_get_domain_for_dev_pasid(group->dev,
>> +							iopf->fault.prm.pasid);
> 
> Do we have a guarantee that the domain is not freed while we handle the
> fault?  We could prevent unbind() while there are pending faults on this
> bond. But a refcount on SVA domains could defer freeing, and would also
> help with keeping the semantics where bind() returns a single refcounted
> bond for any {dev, mm}.
> 
> Given that this path is full of circular locking pitfalls, and to keep the
> fault handler efficient (well, at least not make it worse), we should
> probably keep a getter like iommu_sva_find() that does not require
> locking.

Agreed. We need a mechanism to ensure concurrency. I will look into it.

> 
>> +
>> +		if (!domain || !domain->fault_handler)
>> +			status = IOMMU_PAGE_RESP_INVALID;
>> +
>>   		/*
>>   		 * For the moment, errors are sticky: don't handle subsequent
>>   		 * faults in the group if there is an error.
>>   		 */
>>   		if (status == IOMMU_PAGE_RESP_SUCCESS)
>> -			status = iopf_handle_single(iopf);
>> +			status = domain->fault_handler(&iopf->fault,
>> +						       domain->fault_data);
> 
> If we make this a direct call and only use a light getter for the
> PASID->mm lookup we don't need to look at the domain at all. Or are you
> planning to add external fault handlers?

Yes. I'd like the I/O page fault handling framework to work for
external domains as well, for example, the I/O page faults for user
space page table should be routed to user space.

> 
>>   
>>   		if (!(iopf->fault.prm.flags &
>>   		      IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE))
>> diff --git a/drivers/iommu/iommu-sva-lib.c b/drivers/iommu/iommu-sva-lib.c
>> index 47cf98e661ff..01fa8096bd02 100644
>> --- a/drivers/iommu/iommu-sva-lib.c
>> +++ b/drivers/iommu/iommu-sva-lib.c
>> @@ -87,6 +87,63 @@ static struct iommu_domain *iommu_sva_domain_alloc(struct device *dev)
>>   	return domain;
>>   }
>>   
>> +static enum iommu_page_response_code
>> +iommu_sva_handle_iopf(struct iommu_fault *fault, void *data)
>> +{
>> +	vm_fault_t ret;
>> +	struct mm_struct *mm;
>> +	struct vm_area_struct *vma;
>> +	unsigned int access_flags = 0;
>> +	struct iommu_domain *domain = data;
>> +	unsigned int fault_flags = FAULT_FLAG_REMOTE;
>> +	struct iommu_fault_page_request *prm = &fault->prm;
>> +	enum iommu_page_response_code status = IOMMU_PAGE_RESP_INVALID;
>> +
>> +	if (!(prm->flags & IOMMU_FAULT_PAGE_REQUEST_PASID_VALID))
>> +		return status;
>> +
>> +	mm = domain->sva_cookie;
>> +	if (IS_ERR_OR_NULL(mm))
>> +		return status;
>> +
>> +	mmap_read_lock(mm);
>> +
>> +	vma = find_extend_vma(mm, prm->addr);
>> +	if (!vma)
>> +		/* Unmapped area */
>> +		goto out_put_mm;
>> +
>> +	if (prm->perm & IOMMU_FAULT_PERM_READ)
>> +		access_flags |= VM_READ;
>> +
>> +	if (prm->perm & IOMMU_FAULT_PERM_WRITE) {
>> +		access_flags |= VM_WRITE;
>> +		fault_flags |= FAULT_FLAG_WRITE;
>> +	}
>> +
>> +	if (prm->perm & IOMMU_FAULT_PERM_EXEC) {
>> +		access_flags |= VM_EXEC;
>> +		fault_flags |= FAULT_FLAG_INSTRUCTION;
>> +	}
>> +
>> +	if (!(prm->perm & IOMMU_FAULT_PERM_PRIV))
>> +		fault_flags |= FAULT_FLAG_USER;
>> +
>> +	if (access_flags & ~vma->vm_flags)
>> +		/* Access fault */
>> +		goto out_put_mm;
>> +
>> +	ret = handle_mm_fault(vma, prm->addr, fault_flags, NULL);
>> +	status = ret & VM_FAULT_ERROR ? IOMMU_PAGE_RESP_INVALID :
>> +		IOMMU_PAGE_RESP_SUCCESS;
>> +
>> +out_put_mm:
>> +	mmap_read_unlock(mm);
>> +	mmput(mm);
> 
> mmget_not_zero() is missing since iommu_sva_find() is gone. I'm guessing
> we still need it in case the process dies

Agreed.

> 
> Thanks,
> Jean

Best regards,
baolu
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