Messages in this thread | | | Date | Tue, 15 Mar 2022 11:16:41 +0000 | Subject | Re: [PATCH v2 5/8] iommu: Add PASID support for DMA mapping API users | From | Robin Murphy <> |
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On 2022-03-15 05:07, 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.
Surely the main point of PASIDs is to be able to use more than one of them? The way I expected this to work is that iommu_enable_pasid_dma() returns a *new* struct device representing the dev+PASID combination, and the driver can then pass that to subsequent DMA API and/or IOMMU API calls as normal, and they know to do the right thing. Automatically inferring a PASID for the original physical device clearly can't scale, and seems like a dead-end approach that only helps this one niche use-case.
Either way, I think this is also still fundamentally an IOMMU API operation that belongs in iommu.[ch] - since the iommu_dma_ops consolidation I'd prefer to continue working towards making dma-iommu.h a private header just for IOMMU API internal helpers.
Thanks, Robin.
> 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 > + */ > +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 > + */ > +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. > + */ > +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,
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