[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] PCI Passthrough ARM Design : Draft1
On Wednesday 17 June 2015 06:43 AM, Ian Campbell wrote: On Wed, 2015-06-17 at 13:58 +0100, Stefano Stabellini wrote:Yes, pciback is already capable of doing that, see drivers/xen/xen-pciback/conf_space.cI am not sure if the pci-back driver can query the guest memory map. Is there an existing hypercall ?No, that is missing. I think it would be OK for the virtual BAR to be initialized to the same value as the physical BAR. But I would let the guest change the virtual BAR address and map the MMIO region wherever it wants in the guest physical address space with XENMEM_add_to_physmap_range.I disagree, given that we've apparently survived for years with x86 PV guests not being able to right to the BARs I think it would be far simpler to extend this to ARM and x86 PVH too than to allow guests to start writing BARs which has various complex questions around it. All that's needed is for the toolstack to set everything up and write some new xenstore nodes in the per-device directory with the BAR address/size. Also most guests apparently don't reassign the PCI bus by default, so using a 1:1 by default and allowing it to be changed would require modifying the guests to reasssign. Easy on Linux, but I don't know about others and I imagine some OSes (especially simpler/embedded ones) are assuming the firmware sets up something sane by default. Does the Flow below captures all pointsa) When assigning a device to domU, toolstack creates a node in per device directory with virtual BAR address/size Option1:b) toolstack using some hypercall ask xen to create p2m mapping { virtual BAR : physical BAR } for domU c) domU will not anytime update the BARs, if it does then it is a fault, till we decide how to handle it d) when domU queries BAR address from pci-back the virtual BAR address is provided. Option2:b) domU will not anytime update the BARs, if it does then it is a fault, till we decide how to handle it c) when domU queries BAR address from pci-back the virtual BAR address is provided. d) domU sends a hypercall to map virtual BARs,e) xen pci code reads the BAR and maps { virtual BAR : physical BAR } for domU Which option is better I think Ian is for (2) and Stefano may be (1) Ian. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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