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

[Jacob Pan]

Hi Baolu,

On Sun, 21 May 2023 14:21:25 +0800, Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
wrote:

> 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>
> 
much better, will fix.

Thanks,

Jacob