linux-kernel - Re: [PATCH v4 1/2] iommu/sva: Tighten SVA bind API with explicit flags

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Date:   Wed, 19 May 2021 08:46:08 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     "Luck, Tony" <tony.luck@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "wangzhou1@...ilicon.com" <wangzhou1@...ilicon.com>,
        "zhangfei.gao@...aro.org" <zhangfei.gao@...aro.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v4 1/2] iommu/sva: Tighten SVA bind API with explicit
 flags

Hi Jason,

On Mon, 17 May 2021 11:37:58 -0300, Jason Gunthorpe <jgg@...dia.com> wrote:

> On Thu, May 13, 2021 at 04:40:28PM -0700, Jacob Pan wrote:
> 
> > Looks like we are converging. Let me summarize the takeaways:
> > 1. Remove IOMMU_SVA_BIND_SUPERVISOR flag from this patch, in fact there
> > will be no flags at all for iommu_sva_bind_device()
> > 2. Remove all supervisor SVA related vt-d, idxd code.
> > 3. Create API iommu_setup_system_pasid_direct_map(option_flag)
> > 	if (option_flag == 1)
> > 		iommu_domain_alloc(IOMMU_DOMAIN_DMA);
> > 	if (option_flag == 2)
> > 		iommu_domain_alloc(IOMMU_DOMAIN_DIRECT); //new domain
> > type? setup IOMMU page tables mirroring the direct map
> > 4. Create API iommu_enable_dev_direct_map(struct dev, &pasid, &option)
> > 	- Drivers call this API to get the system PASID and which
> > option is available on the system PASID
> > 	- mark device as PASID only, perhaps a new flag in struct
> > 	device->dev_iommu->pasid_only = 1
> > 5. DMA API IOMMU vendor ops will take action based on the pasid_only
> > flag to decide if the mapping is for system PASID page tables.
> > 
> > Does it make sense?  
> 
> I think you will run into trouble with that approach when you get to
> patches..
> 
> For 'option 1' what you want is an API that is 'give me a PASID that
> is equivalent to the RID'.
> 
> Then all the DMA API operations map IO page tables to both RID and
> PASID access. For the direct mode the PASID and RID will both point at
> the shared all physical memory IO page table.
> 
> Otherwise the DMA API won't care if the device is using RID or PASID,
> if it needs to map a range it does it to the shared IO page table and
> flushes both the RID and PASID based caches.
> 
> Then the driver will use the normal DMA API with its normal struct
> pci_device and simply tell the HW to do DMA TLP's with the returned
> PASID.
> 
> For 'option 2' it should be a completely different API family.
> 
Make sense, thanks for the suggestions.

> Jason


Thanks,

Jacob