[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] 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 +0000, 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@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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