On Thu, Mar 03, 2022 at 02:49:53PM +0000, Jag Raman wrote:
>
>
> > On Mar 2, 2022, at 11:49 AM, Stefan Hajnoczi <stefa...@redhat.com> wrote:
> >
> > On Mon, Feb 28, 2022 at 07:54:38PM +0000, Jag Raman wrote:
> >>
> >>
> >>> On Feb 22, 2022, at 5:40 AM, Stefan Hajnoczi <stefa...@redhat.com> wrote:
> >>>
> >>> On Thu, Feb 17, 2022 at 02:48:59AM -0500, Jagannathan Raman wrote:
> >>>> +struct RemoteIommuElem {
> >>>> + AddressSpace as;
> >>>> + MemoryRegion mr;
> >>>> +};
> >>>> +
> >>>> +GHashTable *remote_iommu_elem_by_bdf;
> >>>
> >>> A mutable global hash table requires synchronization when device
> >>> emulation runs in multiple threads.
> >>>
> >>> I suggest using pci_setup_iommu()'s iommu_opaque argument to avoid the
> >>> global. If there is only 1 device per remote PCI bus, then there are no
> >>> further synchronization concerns.
> >>
> >> OK, will avoid the global. We would need to access the hash table
> >> concurrently since there could be more than one device in the
> >> same bus - so a mutex would be needed here.
> >
> > I thought the PCIe topology can be set up with a separate buf for each
> > x-vfio-user-server? I remember something like that in the previous
> > revision where a root port was instantiated for each x-vfio-user-server.
>
> Yes, we could setup the PCIe topology to be that way. But the user could
> add more than one device to the same bus, unless the bus type explicitly
> limits the number of devices to one (BusClass->max_dev).Due to how the IOMMU is used to restrict the bus to the vfio-user client's DMA mappings, it seems like it's necesssary to limit the number of devices to 1 per bus anyway? Stefan
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