Re: [Xen-devel] [Qemu-devel] [PATCH v3 11/11] igd: move igd-passthrough-isa-bridge creation to machine init
On Fri, 8 Jan 2016, Gerd Hoffmann wrote: > Hi, > > > > That is true. Given that the only qemu-xen codebase with igd support is > > > 4.7 and 4.7 hasn't been released yet, I am OK with changing the guest > > > visible PCI layout. I might ask for your help in backporting the patches > > > ;-) > > What are the 4.7 release plans btw? This is the last development update from the release manager: http://marc.info/?l=qemu-devel&m=145172165010604 * Last posting date: March 18, 2016 * Hard code freeze: April 1, 2016 * RC1: TBD * Release: June 3, 2016 ___ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
Re: [Xen-devel] [Qemu-devel] [PATCH v3 11/11] igd: move igd-passthrough-isa-bridge creation to machine init
Hi, > > That is true. Given that the only qemu-xen codebase with igd support is > > 4.7 and 4.7 hasn't been released yet, I am OK with changing the guest > > visible PCI layout. I might ask for your help in backporting the patches > > ;-) What are the 4.7 release plans btw? > One thing that I forgot to consider is that QEMU 2.5 has been released > with igd passthrough too and Xen 4.6 + QEMU 2.5 is a combination we > should support. > > However QEMU 2.5 has a serious bug > (http://marc.info/?l=qemu-devel&m=145172165010604) which probably > prevents igd passthrough from working at all. Stumbled over that one too, so my series has a (different) fix for it as well. > I asked Xudong to investigate. I am thinking that if the feature > works in 2.5, we need to support it, therefore we cannot break > migration by changing the PCI layout. I'd expect it is broken (at least for older guests). In case 2.5 works fine as-is we should be able to ditch TYPE_IGD_PASSTHROUGH_I440FX_PCI_DEVICE altogether b/c it is a no-op in 2.5 because of the bug. But lets wait for the test results ... > Otherwise if the feature doesn't work, we could take the liberty to > make the change. Do you agree? Yes. cheers, Gerd ___ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
Re: [Xen-devel] [Qemu-devel] [PATCH v3 11/11] igd: move igd-passthrough-isa-bridge creation to machine init
On Fri, 8 Jan 2016, Stefano Stabellini wrote: > > > > xen_pt_initfn checks that igd-passthru=on is set in case it finds a igd > > > > device is assigned, that will make sure the igd-isa-bridge is present. > > > > > > > > But, yes, you can create a igd-isa-bridge now even when not assigning a > > > > igd device, either by specifying igd-passthru=on or using -device. I > > > > fail to see why this is a problem though, care to explain? > > > > > > It is going to change the PCI layout of any virtual machines with a > > > config file containing > > > > > > gfx_passthru="igd" > > > > > > and no pci config line. A Xen 4.7 user could add gfx_passthru="igd" to > > > all her VM config files, because actually it does nothing unless an > > > Intel graphic card is assigned to the VM. > > > > No. It changes the host bridge even when not passing through a igd, > > because that is linked to igd-passthru=on only. > > > > So making both host bridge tweak and isa bridge tweak triggered by > > igd-passthru=on brings more consistency to the whole thing. > > That is true. Given that the only qemu-xen codebase with igd support is > 4.7 and 4.7 hasn't been released yet, I am OK with changing the guest > visible PCI layout. I might ask for your help in backporting the patches > ;-) One thing that I forgot to consider is that QEMU 2.5 has been released with igd passthrough too and Xen 4.6 + QEMU 2.5 is a combination we should support. However QEMU 2.5 has a serious bug (http://marc.info/?l=qemu-devel&m=145172165010604) which probably prevents igd passthrough from working at all. I asked Xudong to investigate. I am thinking that if the feature works in 2.5, we need to support it, therefore we cannot break migration by changing the PCI layout. Otherwise if the feature doesn't work, we could take the liberty to make the change. Do you agree? ___ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
Re: [Xen-devel] [Qemu-devel] [PATCH v3 11/11] igd: move igd-passthrough-isa-bridge creation to machine init
On Thu, 7 Jan 2016, Gerd Hoffmann wrote: > On Do, 2016-01-07 at 13:10 +, Stefano Stabellini wrote: > > CC'ing the Xen x86 maintainers > > > > On Thu, 7 Jan 2016, Gerd Hoffmann wrote: > > > Hi, > > > > > > > One thing I don't like about this is that it is going to skip the checks > > > > done in xen_pt_initfn. > > > > > > Hmm? Those checks are still done when you assign a igd ... > > > > Their failure doesn't affect the creation of the bridge. > > Doesn't their failure makes qemu throw a fatal error and exit? > So the guest isn't going to run either way? No, it doesn't. QEMU doesn't even print an error message. > > > > For example it is going to create the isa bridge, > > > > even if there is going to be an error loading the vga bios or if the > > > > device specified is not even an Intel graphic card. > > > > > > Creating the special igd-isa-bridge is no longer tied to actually > > > assigning a igd, but to the igd-passthru=on machine option being present > > > (and machine type being 'pc'). > > > > and machine type 'xenfv', unless I am mistaken? > > Yes, xenfv too (uses i440fx too and thus is a 'pc' derivate). Good > > > xen_pt_initfn checks that igd-passthru=on is set in case it finds a igd > > > device is assigned, that will make sure the igd-isa-bridge is present. > > > > > > But, yes, you can create a igd-isa-bridge now even when not assigning a > > > igd device, either by specifying igd-passthru=on or using -device. I > > > fail to see why this is a problem though, care to explain? > > > > It is going to change the PCI layout of any virtual machines with a > > config file containing > > > > gfx_passthru="igd" > > > > and no pci config line. A Xen 4.7 user could add gfx_passthru="igd" to > > all her VM config files, because actually it does nothing unless an > > Intel graphic card is assigned to the VM. > > No. It changes the host bridge even when not passing through a igd, > because that is linked to igd-passthru=on only. > > So making both host bridge tweak and isa bridge tweak triggered by > igd-passthru=on brings more consistency to the whole thing. That is true. Given that the only qemu-xen codebase with igd support is 4.7 and 4.7 hasn't been released yet, I am OK with changing the guest visible PCI layout. I might ask for your help in backporting the patches ;-) > > > Also note that moving this to machine init nicely handles the fact that > > > the igd-isa-bridge is needed on 'pc' only, not on 'q35'. If you don't > > > want create the igd-isa-bridge in machine init, what is your alternative > > > suggestion to handle this? > > > > Maybe we could retain the check whether an Intel graphic card has been > > assigned? > > Should be possible, but is not that easy due to initialization order > issues. ___ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
