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Date: Wed, 21 Jul 2021 12:12:10 +0100 From: Robin Murphy <robin.murphy@....com> To: Lu Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>, Sanjay Kumar <sanjay.k.kumar@...el.com>, Kevin Tian <kevin.tian@...el.com>, Ashok Raj <ashok.raj@...el.com>, Jacob Pan <jacob.jun.pan@...ux.intel.com>, Dave Jiang <dave.jiang@...el.com>, Liu Yi L <yi.l.liu@...el.com> Cc: iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 4/5] iommu/vt-d: Disallow SVA if devices don't support 64-bit address On 2021-07-21 02:50, Lu Baolu wrote: > Hi Robin, > > Thanks a lot for reviewing my patch! > > On 7/20/21 5:27 PM, Robin Murphy wrote: >> On 2021-07-20 02:38, Lu Baolu wrote: >>> When the device and CPU share an address space (such as SVA), the device >>> must support the same addressing capability as the CPU. The CPU does not >>> consider the addressing ability of any device when managing the page >>> table >>> of a process, so the device must have enough addressing ability to bind >>> the page table of the process. >>> >>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com> >>> --- >>> drivers/iommu/intel/iommu.c | 3 +++ >>> 1 file changed, 3 insertions(+) >>> >>> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c >>> index f45c80ce2381..f3cca1dd384d 100644 >>> --- a/drivers/iommu/intel/iommu.c >>> +++ b/drivers/iommu/intel/iommu.c >>> @@ -5372,6 +5372,9 @@ static int intel_iommu_enable_sva(struct device >>> *dev) >>> if (!(iommu->flags & VTD_FLAG_SVM_CAPABLE)) >>> return -ENODEV; >>> + if (!dev->dma_mask || *dev->dma_mask != DMA_BIT_MASK(64)) >> >> Careful - VFIO doesn't set DMA masks (since it doesn't use the DMA API), > > SVA doesn't work through the VFIO framework. Did anyone say it does? My point is that, as far as I understand, the SVA UAPI is very much intended to work *with* VFIO, and even if the finer details are still mired in the /dev/ioasid discussion today we should definitely expect to see VFIO-like use-cases at some point. I certainly don't see why any of the guest SVA stuff exists already if not for VFIO-assigned devices? >> so this appears to be relying on another driver having bound previously, > > Yes. You are right. > >> otherwise the mask would still be the default 32-bit one from >> pci_setup_device(). I'm not sure that's an entirely robust assumption. > > Currently SVA implementation always requires a native kernel driver. The > assumption is that the drivers should check and set 64-bit addressing > capability before calling iommu_sva_xxx() APIs. ...and given that that is not a documented requirement, and certainly not a technical one (even a self-contained kernel driver could choose to only use SVA contexts and not touch the DMA API), it's an inherently fragile assumption which I'm confident *will* be broken eventually :) Robin. >>> + return -ENODEV; >>> + >>> if (intel_iommu_enable_pasid(iommu, dev)) >>> return -ENODEV; >>> > > Best regards, > baolu
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