[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] PCI Passthrough ARM Design : Draft1
On Wed, Jun 17, 2015 at 03:35:02PM +0100, Stefano Stabellini wrote: > On Wed, 17 Jun 2015, Ian Campbell wrote: > > On Wed, 2015-06-17 at 07:14 -0700, Manish Jaggi wrote: > > > > > > 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.c > > > >> > > > >>> I 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 points > > > a) 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 > > > > As Julien has noted pciback already deals with this correctly, because > > sizing a BAR involves a write, it implementes a scheme which allows > > either the hardcoded virtual BAR to be written or all 1s (needed for > > size detection). > > > > > 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) > > > > In fact I'm now (after Julien pointed out the current behaviour of > > pciback) in favour of (1), although I'm not sure if Stefano is too. > > > > (I was never in favour of (2), FWIW, I previously was in favour of (3) > > which is like (2) except pciback makes the hypervcall to map the virtual > > bars to the guest, I'd still favour that over (2) but (1) is now my > > preference) > > OK, let's go with (1). Right, and as the maintainer of pciback that means I don't have to do anything right :-) _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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