[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Multi-bridged PCIe devices (Was: Re: iommuu/vt-d issues with LSI MegaSAS (PERC5i))
On Wed, Sep 11, 2013 at 01:19:44PM +0100, Gordan Bobic wrote: > On Wed, 11 Sep 2013 12:57:10 +0100, "Jan Beulich" > <JBeulich@xxxxxxxx> wrote: > >>>>On 11.09.13 at 13:44, Gordan Bobic <gordan@xxxxxxxxxx> wrote: > >>This got me thinking - if the problem is broken IOMMU > >>implementation, > >> is the IOMMU _actually_ required for PCI passthrough to HVM > >> guests if all the memory holes and BARs are made exactly the same > >> in dom0 and domU? If vBAR=pBAR, then surely there is no memory > >> range remapping to be done anyway - which means that there > >> is no need for the strict IOMMU requirements (over and above > >> the requirements and caveats of PV domUs). > > > >But with this you ignore the need to handle device bus mastering > >activities. In order to work without IOMMU, the guest's memory > >addresses would also require guest-physical = machine-physical. > > Hmm... that would be harder to achieve, mainly due to legacy > stuff like base memory. But if (fingers crossed) DMA doesn't > occur below 1MB, maybe the map can be bodged to emulate the > addresses below 1MB, carve out as small a chunk of 32-bit > memory as we can get away with for each guest, and map the > rest with vmem=pmem in 64-bit memory range. But you are > right - that gets way more complicated than I originally > envisaged - all for the sake of supporting legacy > and Steam boot-loader systems. :( > I don't know the details but many years ago there was a patch to allow PCI passthru to HVM guests without an IOMMU.. I think it's linked on Xen pcipassthrough wiki page. It had a limitation that only one HVM guest was supported for PCI passthru. -- Pasi _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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