Re: [PATCH v6 2/4] iommu: Move global PASID allocation from SVA to core

[Baolu Lu]

On 5/20/23 4:32 AM, Jacob Pan wrote:
> Global PASID can be used beyond SVA. For example, drivers that use
> Intel ENQCMD to submit work must use global PASIDs in that PASID
> is stored in a per CPU MSR. When such device need to submit work
> for in-kernel DMA with PASID, it must allocate PASIDs from the same
> global number space to avoid conflict.
>
> This patch moves global PASID allocation APIs from SVA to IOMMU APIs.
> Reserved PASIDs, currently only RID_PASID, are excluded from the global
> PASID allocation.
>
> It is expected that device drivers will use the allocated PASIDs to
> attach to appropriate IOMMU domains for use.
>
> Signed-off-by: Jacob Pan<jacob.jun.pan@xxxxxxxxxxxxxxx>
> ---
> v6: explicitly exclude reserved a range from SVA PASID allocation
>      check mm PASID compatibility with device
> v5: move PASID range check inside API so that device drivers only pass
>      in struct device* (Kevin)
> v4: move dummy functions outside ifdef CONFIG_IOMMU_SVA (Baolu)
> ---
>   drivers/iommu/iommu-sva.c | 33 ++++++++++++++-------------------
>   drivers/iommu/iommu.c     | 24 ++++++++++++++++++++++++
>   include/linux/iommu.h     | 10 ++++++++++
>   3 files changed, 48 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
> index 9821bc44f5ac..7fe8e977d8eb 100644
> --- a/drivers/iommu/iommu-sva.c
> +++ b/drivers/iommu/iommu-sva.c
> @@ -10,33 +10,33 @@
>   #include "iommu-sva.h"
>   
>   static DEFINE_MUTEX(iommu_sva_lock);
> -static DEFINE_IDA(iommu_global_pasid_ida);
>   
>   /* Allocate a PASID for the mm within range (inclusive) */
> -static 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, struct device *dev)
>   {
> +	ioasid_t pasid;
>   	int ret = 0;
>   
> -	if (min == IOMMU_PASID_INVALID ||
> -	    max == IOMMU_PASID_INVALID ||
> -	    min == 0 || max < min)
> -		return -EINVAL;
> -
>   	if (!arch_pgtable_dma_compat(mm))
>   		return -EBUSY;
>   
>   	mutex_lock(&iommu_sva_lock);
>   	/* Is a PASID already associated with this mm? */
>   	if (mm_valid_pasid(mm)) {
> -		if (mm->pasid < min || mm->pasid > max)
> -			ret = -EOVERFLOW;
> +		if (mm->pasid <= dev->iommu->max_pasids)
> +			goto out;
> +		dev_err(dev, "current mm PASID %d exceeds device range %d!",
> +			mm->pasid, dev->iommu->max_pasids);
> +		ret = -ERANGE;
>   		goto out;
>   	}

Nit: Above is just refactoring, so it's better to keep the code behavior
consistent. For example, no need to change the error# from -EOVERFLOW to
-ERANGE, and no need to leave a new kernel message.

Anyway, if you think these changes are helpful, it's better to have them
in separated patches.

In the end, perhaps we can simply have code like this:

	if (mm_valid_pasid(mm)) {
		if (mm->pasid > dev->iommu->max_pasids)
			ret = -EOVERFLOW;
		goto out;
	}

Others look good to me, with above addressed,

Reviewed-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>

Best regards,
baolu