Re: [PATCH v4 3/6] iommu/sva: Stop using ioasid_set for SVA

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

On 3/3/23 1:17 AM, Jacob Pan wrote:
> Hi Baolu,
> 
> On Thu, 2 Mar 2023 21:01:42 +0800, Baolu Lu <baolu.lu@linux.intel.com>
> wrote:
> 
>> On 2023/3/2 7:56, Jacob Pan wrote:
>>> From: Jason Gunthorpe <jgg@nvidia.com>
>>>
>>> Instead SVA drivers can use a simple global IDA to allocate PASIDs for
>>> each mm_struct.
>>>
>>> Future work would be to allow drivers using the SVA APIs to reserve
>>> global PASIDs from this IDA for their internal use, eg with the DMA API
>>> PASID support.
>>>
>>> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
>>> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
>>> ---
>>> v4:
>>> 	- Keep GFP_ATOMIC flag for PASID allocation, will changed to
>>> 	GFP_KERNEL in a separate patch.
>>> ---
>>>    drivers/iommu/iommu-sva.c | 62 ++++++++++-----------------------------
>>>    drivers/iommu/iommu-sva.h |  3 --
>>>    2 files changed, 15 insertions(+), 50 deletions(-)
>>>
>>> diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
>>> index 376b2a9e2543..297852ae5e7c 100644
>>> --- a/drivers/iommu/iommu-sva.c
>>> +++ b/drivers/iommu/iommu-sva.c
>>> @@ -9,26 +9,13 @@
>>>    #include "iommu-sva.h"
>>>    
>>>    static DEFINE_MUTEX(iommu_sva_lock);
>>> -static DECLARE_IOASID_SET(iommu_sva_pasid);
>>> +static DEFINE_IDA(iommu_global_pasid_ida);
>>>    
>>> -/**
>>> - * iommu_sva_alloc_pasid - Allocate a PASID for the mm
>>> - * @mm: the mm
>>> - * @min: minimum PASID value (inclusive)
>>> - * @max: maximum PASID value (inclusive)
>>> - *
>>> - * Try to allocate a PASID for this mm, or take a reference to the
>>> existing one
>>> - * provided it fits within the [@min, @max] range. On success the
>>> PASID is
>>> - * available in mm->pasid and will be available for the lifetime of
>>> the mm.
>>> - *
>>> - * Returns 0 on success and < 0 on error.
>>> - */
>>> -int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t
>>> max) +static int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t
>>> min, ioasid_t max) {
>>> -	int ret = 0;
>>> -	ioasid_t pasid;
>>> +	int ret;
>>>    
>>> -	if (min == INVALID_IOASID || max == INVALID_IOASID ||
>>> +	if (min == IOMMU_PASID_INVALID || max == IOMMU_PASID_INVALID ||
>>>    	    min == 0 || max < min)
>>
>> It's irrelevant to this patch. Just out of curiosity, why do we need to
>> exclude PASID 0 here? I just had a quick look at PCI spec section 6.20.
>> The spec does not state that PASID 0 is invalid.
>>
> my understanding is that ARM reserves PASID0, unlike VT-d where RID_PASID
> is programmable.

I suppose the common thing is reserving some kind of special PASIDs.

> 
>>>    		return -EINVAL;
>>>    
>>> @@ -37,39 +24,20 @@ int iommu_sva_alloc_pasid(struct mm_struct *mm,
>>> ioasid_t min, ioasid_t max) if (pasid_valid(mm->pasid)) {
>>>    		if (mm->pasid < min || mm->pasid >= max)
>>>    			ret = -EOVERFLOW;
>>> +		else
>>> +			ret = 0;
>>
>> Nit:
>>
>> If you didn't change "int ret = 0" to "int ret", we don't need above two
>> lines. Did I miss anything?
>>
> you are right
> 
>>>    		goto out;
>>>    	}
>>>    
>>> -	pasid = ioasid_alloc(&iommu_sva_pasid, min, max, mm);
>>> -	if (!pasid_valid(pasid))
>>> -		ret = -ENOMEM;
>>> -	else
>>> -		mm->pasid = ret;
>>> +	ret = ida_alloc_range(&iommu_global_pasid_ida, min, max,
>>> GFP_ATOMIC);
>>> +	if (ret < min)
>>
>> Nit:
>> 	    ret < 0?
> will do
> 
>> ida_alloc_range() returns negative error number on failure.
>>
>>> +		goto out;
>>> +	mm->pasid = ret;
>>> +	ret = 0;
>>>    out:
>>>    	mutex_unlock(&iommu_sva_lock);
>>>    	return ret;
>>>    }
>>> -EXPORT_SYMBOL_GPL(iommu_sva_alloc_pasid);
>>> -
>>> -/* ioasid_find getter() requires a void * argument */
>>> -static bool __mmget_not_zero(void *mm)
>>> -{
>>> -	return mmget_not_zero(mm);
>>> -}
>>> -
>>> -/**
>>> - * iommu_sva_find() - Find mm associated to the given PASID
>>> - * @pasid: Process Address Space ID assigned to the mm
>>> - *
>>> - * On success a reference to the mm is taken, and must be released
>>> with mmput().
>>> - *
>>> - * Returns the mm corresponding to this PASID, or an error if not
>>> found.
>>> - */
>>> -struct mm_struct *iommu_sva_find(ioasid_t pasid)
>>> -{
>>> -	return ioasid_find(&iommu_sva_pasid, pasid, __mmget_not_zero);
>>> -}
>>> -EXPORT_SYMBOL_GPL(iommu_sva_find);
>>
>> Removing iommu_sva_find() has nothing to do with the intention of this
>> patch. Perhaps make it in a separated patch?
> will do
> 
>>>    
>>>    /**
>>>     * iommu_sva_bind_device() - Bind a process address space to a device
>>> @@ -241,8 +209,8 @@ iommu_sva_handle_iopf(struct iommu_fault *fault,
>>> void *data)
>>>    void mm_pasid_drop(struct mm_struct *mm)
>>>    {
>>> -	if (pasid_valid(mm->pasid)) {
>>> -		ioasid_free(mm->pasid);
>>> -		mm->pasid = INVALID_IOASID;
>>> -	}
>>> +	if (likely(!pasid_valid(mm->pasid)))
>>
>> Why is this a likely?
> most mm does not have a PASID, thus initialized with invalid ioasid during
> fork. This function is called for every mm.

Make sense.

> 
>>> +		return;
>>> +
>>> +	ida_free(&iommu_global_pasid_ida, mm->pasid);
>>>    }
>>> diff --git a/drivers/iommu/iommu-sva.h b/drivers/iommu/iommu-sva.h
>>> index 7215a761b962..c22d0174ad61 100644
>>> --- a/drivers/iommu/iommu-sva.h
>>> +++ b/drivers/iommu/iommu-sva.h
>>> @@ -8,9 +8,6 @@
>>>    #include <linux/ioasid.h>
>>>    #include <linux/mm_types.h>
>>>    
>>> -int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t
>>> max); -struct mm_struct *iommu_sva_find(ioasid_t pasid);
>>> -
>>>    /* I/O Page fault */
>>>    struct device;
>>>    struct iommu_fault;
>>
>> Best regards,
>> baolu
> 
> 
> Thanks,
> 
> Jacob

Best regards,
baolu