Messages in this thread | | | From | Lu Baolu <> | Subject | Re: [PATCH 4/5] iommu/vt-d: Disallow SVA if devices don't support 64-bit address | Date | Wed, 21 Jul 2021 22:17:18 +0800 |
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On 2021/7/21 19:12, Robin Murphy wrote: > 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@linux.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?
Agreed. From /dev/ioasid design point of view, it's possible to have VFIO-like use case of SVA. Perhaps the device addressing capability could be included in GET_DEV_INFO of /dev/ioasid UAPI.
> >>> 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 :) >
Fair enough. I will drop this patch.
Thanks a lot for the comments.
Best regards, baolu
> Robin. > >>>> + return -ENODEV; >>>> + >>>> if (intel_iommu_enable_pasid(iommu, dev)) >>>> return -ENODEV; >>>> >> >> Best regards, >> baolu
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