Messages in this thread | | | Subject | Re: [PATCH v3 2/3] uio_pci_generic: add MSI/MSI-X support | From | Avi Kivity <> | Date | Thu, 8 Oct 2015 12:44:09 +0300 |
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On 10/08/2015 12:16 PM, Michael S. Tsirkin wrote: > On Thu, Oct 08, 2015 at 11:46:30AM +0300, Avi Kivity wrote: >> >> On 10/08/2015 10:32 AM, Michael S. Tsirkin wrote: >>> On Thu, Oct 08, 2015 at 08:33:45AM +0300, Avi Kivity wrote: >>>> It is good practice to defend against root oopsing the kernel, but in some >>>> cases it cannot be achieved. >>> Absolutely. That's one of the issues with these patches. They don't even >>> try where it's absolutely possible. >>> >> Are you referring to blocking the maps of the msix BAR areas? > For example. There are more. I listed some of the issues on the mailing > list, and I might have missed some. VFIO has code to address all this, > people should share code to avoid duplication, or at least read it > to understand the issues.
All but one of those are unrelated to the patch that adds msix support.
> >> I think there is value in that. The value is small because a >> corruption is more likely in the dynamic memory responsible for tens >> of millions of DMA operations per second, rather than a static 4K >> area, but it exists. > There are other bugs which will hurt e.g. each time application does not > exit gracefully.
uio_pci_generic disables DMA when the device is removed, so we're safe here, at least if files are released before the address space.
> > But well, heh :) That's precisely my feeling about the whole "running > userspace drivers without an IOMMU" project. The value is small > since modern hardware has fast IOMMUs, but it exists. >
For users that don't have iommus at all (usually because it is taken by the hypervisor), it has great value.
I can't comment on iommu overhead; for my use case it is likely negligible and we will use an iommu when available; but apparently it matters for others.
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