Re: [PATCH v2 5/8] iommu: Add PASID support for DMA mapping API users

[Jacob Pan <jacob.jun.pan@linux.intel.com>]

Hi BaoLu,

On Fri, 18 Mar 2022 20:43:54 +0800, Lu Baolu <baolu.lu@linux.intel.com>
wrote:

> On 2022/3/15 13:07, Jacob Pan wrote:
> > DMA mapping API is the de facto standard for in-kernel DMA. It operates
> > on a per device/RID basis which is not PASID-aware.
> > 
> > Some modern devices such as Intel Data Streaming Accelerator, PASID is
> > required for certain work submissions. To allow such devices use DMA
> > mapping API, we need the following functionalities:
> > 1. Provide device a way to retrieve a PASID for work submission within
> > the kernel
> > 2. Enable the kernel PASID on the IOMMU for the device
> > 3. Attach the kernel PASID to the device's default DMA domain, let it
> > be IOVA or physical address in case of pass-through.
> > 
> > This patch introduces a driver facing API that enables DMA API
> > PASID usage. Once enabled, device drivers can continue to use DMA APIs
> > as is. There is no difference in dma_handle between without PASID and
> > with PASID.
> > 
> > Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > ---
> >   drivers/iommu/dma-iommu.c | 65 +++++++++++++++++++++++++++++++++++++++
> >   include/linux/dma-iommu.h |  7 +++++
> >   include/linux/iommu.h     |  9 ++++++
> >   3 files changed, 81 insertions(+)
> > 
> > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> > index b22034975301..d0ff1a34b1b6 100644
> > --- a/drivers/iommu/dma-iommu.c
> > +++ b/drivers/iommu/dma-iommu.c
> > @@ -39,6 +39,8 @@ enum iommu_dma_cookie_type {
> >   	IOMMU_DMA_MSI_COOKIE,
> >   };
> >   
> > +static DECLARE_IOASID_SET(iommu_dma_pasid);
> > +
> >   struct iommu_dma_cookie {
> >   	enum iommu_dma_cookie_type	type;
> >   	union {
> > @@ -370,6 +372,69 @@ void iommu_put_dma_cookie(struct iommu_domain
> > *domain) domain->iova_cookie = NULL;
> >   }
> >   
> > +/**
> > + * iommu_enable_pasid_dma --Enable in-kernel DMA request with PASID
> > + * @dev:	Device to be enabled
> > + *
> > + * DMA request with PASID will be mapped the same way as the legacy
> > DMA.
> > + * If the device is in pass-through, PASID will also pass-through. If
> > the
> > + * device is in IOVA map, the supervisor PASID will point to the same
> > IOVA
> > + * page table.
> > + *
> > + * @return the kernel PASID to be used for DMA or INVALID_IOASID on
> > failure  
> 
> The comment on the return value should be rephrased according to the
> real code.
> 
yes, will do.

> > + */
> > +int iommu_enable_pasid_dma(struct device *dev, ioasid_t *pasid)
> > +{
> > +	struct iommu_domain *dom;
> > +	ioasid_t id, max;
> > +	int ret;
> > +
> > +	dom = iommu_get_domain_for_dev(dev);
> > +	if (!dom || !dom->ops || !dom->ops->attach_dev_pasid)
> > +		return -ENODEV;
> > +	max = iommu_get_dev_pasid_max(dev);
> > +	if (!max)
> > +		return -EINVAL;
> > +
> > +	id = ioasid_alloc(&iommu_dma_pasid, 1, max, dev);
> > +	if (id == INVALID_IOASID)
> > +		return -ENOMEM;
> > +
> > +	ret = dom->ops->attach_dev_pasid(dom, dev, id);
> > +	if (ret) {
> > +		ioasid_put(id);
> > +		return ret;
> > +	}
> > +	*pasid = id;
> > +
> > +	return ret;
> > +}
> > +EXPORT_SYMBOL(iommu_enable_pasid_dma);
> > +
> > +/**
> > + * iommu_disable_pasid_dma --Disable in-kernel DMA request with PASID
> > + * @dev:	Device's PASID DMA to be disabled
> > + *
> > + * It is the device driver's responsibility to ensure no more incoming
> > DMA
> > + * requests with the kernel PASID before calling this function. IOMMU
> > driver
> > + * ensures PASID cache, IOTLBs related to the kernel PASID are cleared
> > and
> > + * drained.
> > + *
> > + * @return 0 on success or error code on failure  
> 
> Ditto.
> 
same

> > + */
> > +void iommu_disable_pasid_dma(struct device *dev, ioasid_t pasid)
> > +{
> > +	struct iommu_domain *dom;
> > +
> > +	/* TODO: check the given PASID is within the ioasid_set */
> > +	dom = iommu_get_domain_for_dev(dev);
> > +	if (!dom->ops->detach_dev_pasid)
> > +		return;
> > +	dom->ops->detach_dev_pasid(dom, dev, pasid);
> > +	ioasid_put(pasid);
> > +}
> > +EXPORT_SYMBOL(iommu_disable_pasid_dma);
> > +
> >   /**
> >    * iommu_dma_get_resv_regions - Reserved region driver helper
> >    * @dev: Device from iommu_get_resv_regions()
> > diff --git a/include/linux/dma-iommu.h b/include/linux/dma-iommu.h
> > index 24607dc3c2ac..e6cb9b52a420 100644
> > --- a/include/linux/dma-iommu.h
> > +++ b/include/linux/dma-iommu.h
> > @@ -18,6 +18,13 @@ int iommu_get_dma_cookie(struct iommu_domain
> > *domain); int iommu_get_msi_cookie(struct iommu_domain *domain,
> > dma_addr_t base); void iommu_put_dma_cookie(struct iommu_domain
> > *domain); 
> > +/*
> > + * For devices that can do DMA request with PASID, setup a system
> > PASID.
> > + * Address modes (IOVA, PA) are selected by the platform code.
> > + */  
> 
> No need for a comment here. Or move it to the function if need.
> 
right, this comment is obsolete. will remove.

> > +int iommu_enable_pasid_dma(struct device *dev, ioasid_t *pasid);
> > +void iommu_disable_pasid_dma(struct device *dev, ioasid_t pasid);
> > +
> >   /* Setup call for arch DMA mapping code */
> >   void iommu_setup_dma_ops(struct device *dev, u64 dma_base, u64
> > dma_limit); int iommu_dma_init_fq(struct iommu_domain *domain);
> > diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> > index fde5b933dbe3..fb011722e4f8 100644
> > --- a/include/linux/iommu.h
> > +++ b/include/linux/iommu.h
> > @@ -395,6 +395,15 @@ static inline void iommu_set_dev_pasid_max(struct
> > device *dev, 
> >   	param->pasid_max = max;
> >   }
> > +static inline ioasid_t iommu_get_dev_pasid_max(struct device *dev)
> > +{
> > +	struct dev_iommu *param = dev->iommu;
> > +
> > +	if (WARN_ON(!param))
> > +		return 0;
> > +
> > +	return param->pasid_max;
> > +}
> >   
> >   int iommu_device_register(struct iommu_device *iommu,
> >   			  const struct iommu_ops *ops,  
> 
> Best regards,
> baolu


Thanks,

Jacob
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