On Mon, Mar 21, 2016 at 9:43 PM, Zir Blazer <zir_bla...@hotmail.com> wrote: > I'm sure I asked this before and was expecting AW tehnical response, but > instead he said "TL;DR" since it was in a ridiculous long mail with a > multitude of other questions. But now I need a response since I plan to do > this next week, so I have to try again. > > > I have readed this numerous times and still think its missing one or two > examples to understand it better... > > http://vfio.blogspot.com.ar/2014/08/whats-deal-with-vga-arbitration.html > > As far that I managed to understand, the VGA Arbitration is an issue when you > have two or more Devices that wants to use the legacy VGA protocol (Including > both host and VM passthroughed Devices), which is a phase that usually only > last until the OS loads the GPU Drivers and disables it. This is fine. > However, there are some thing that are missing... > > > 1) My current setup includes a Haswell platform with the Intel IGP, and a > Radeon 5770 from before UEFI GOP became available, so it is legacy VBIOS only. > > I understand that OVMF allows you to load a Video Card PCI Option ROM with > UEFI GOP at VM POST time, in which case, you can see OVMF POSTing in the > Monitor attached to the passthroughed Video Card, and that is called Primary > VGA Passthrough. SeaBIOS can do the same loading a legacy VBIOS PCI Option > ROM during POST. This phase last during the boot process until the OS GPU > Drivers takes over, and at that point, both BIOS/UEFI Boot converge since the > Drivers should disable VGA. The advantage of the pure UEFI Boot method is > that VGA is not used during boot, so you don't count it at any point for VGA > Arbitration purposes. However, this should apply for UEFI Boot in the host, > too. > > Since I do passthrough of the Radeon 5770 to a Windows VM, I will have to use > SeaBIOS with legacy VBIOS and VGA for booting if doing Primary VGA > Passthrough, but the host GPU has no need for VGA at all. The Intel IGP has > available UEFI GOP support (At least since Ivy Bridge I think, but Haswell > absolutely has it since that's my platform and I can confirm it), so I can do > a pure UEFI Boot with no CSM for the host. VGA should not be used at all for > the Intel IGP, which means that I have the legacy VGA protocol exclusively > for the Radeon 5770 VM, so I should be able to create it using SeaBIOS and > load the Video Card legacy VBIOS, and expect it to do Primary VGA Passthrough > without having to deal with VGA Arbitration issues. Is this correct? > > What makes me doubt is that you mention that the mechanism for Intel IGP > Drivers to opt out of VGA Arbitration seems to be broken, but you blogged > that before OVMF took over, and make no mention regardless if that applies to > host BIOS Boot with Intel IGP, or BOTH BIOS and UEFI Boot. This is important > to me since I have a Radeon 5770 from before they started to incorporate UEFI > GOP support, so for Primary VGA Passthrough I have to use SeaBIOS. > > > 2) What about Secondary VGA Passthrough? In the case of my current setup > using Xen, the VM POST in a SDL window in the host screen, then switchs to > the Monitor attached to the VM when Windows begins loading. This means that > VGA isn't used either, since no VBIOS is loaded at all, through that also > means that the Video Card is useless without the OS Drivers. So, can VFIO > also do Secondary VGA Passthrough? I barely recall seeing it mentioned. > > Truth be told, for as long as when we reach the convengence point after the > OS loads the Drivers everything works as intended, how I get there seems like > a detail that doesn't really matters. If I can use an emulated VGA for VM > POST and boot, then switch to the passthroughed Video Card, I don't see it as > a con of Secondary VGA Passthrough and would say that it is a slighty easier > method. The main advantage being that it should be universal regardless if > the host is doing BIOS or UEFI Boot, there is another VM using a > passthroughed Video Card using legacy VBIOS, etc, since it simply doesn't > care for those details. > > > 3) What are the issues with Intel IGP Passthrough and VFIO? I'm not intending > to do it since it would be worse than my Radeon 5770, but I'm curious. If I > recall correctly, there were issues with it on Xen that required patches, > since it seems that either it or the Drivers are expecting for the IGP to sit > on PCI Address 00:02.0, so when doing IGP Passthrough, that address got > reserved for it. Isn't possible to workaround this currently in standalone > QEMU? Can't see why you wouldn't be able to use -nodefaults, then plug in > -device vfio-pci,bus=pcie.0,addr=02.0,host=00:02.0, or something like that. > If it requires a PCIe Root Complex and can't be workarounded for the i440FX > PCI Host Bridge, then maybe it works on Q35. I was intending to try this when > I deploy standalone QEMU, but I would like to hear the technical explanation. > > > 4) What should be the success chance of modding a VBIOS to add UEFI GOP > support and use it for OVMF? At some point I was intending to do that mod for > my Radeon 5770, but after tons of googling, I found other users claiming that > it had a peculiar issue: The ROM was too small. It is a 64 KiB Flash ROM, > while the resulting binary after performing the mod handily surpassed that > size. But I think that I saw smaller cards like Radeons 5450 successfully > modded adding UEFI GOP, through the guys that performed it were interesed in > using them for MAC platforms or Windows 8 Fast Boot, no one was interesed in > OVMF UEFI Boot. > > Now, I know that QEMU supports a romfile= parameter that would allow me to > replace the default PCI Option ROM with something else. Would it be possible > to load a bigger file? Without the ROM size constrains, the UEFI GOP modding > could actually be useful. Heck, it would be absolutely wonderful if someone > can develop a way to consistently perform such mod on a given VBIOS, since it > would be THE ABSOLUTE SAVIOR of all the legacy Video Cards users, stomping > VGA Arbitration and anything else along the way. Heck, you don't even have to > actually flash the ROM to try if it works or not. This sounds at least > wonderful on paper, but would like to know if someone tried, succeded, or > believes that being able to load a ROM is as good as I think it is. > > > I expect to get AW to reply this time, heh. Seriously, I can't make wall of > texts smaller than this since i always try to explain context and my thoughs. > > _______________________________________________ > vfio-users mailing list > vfio-users@redhat.com > https://www.redhat.com/mailman/listinfo/vfio-users
I think I was in a similar situation before. I am using Haswell CPU with its integrated graphics for host OS booted on UEFI board. I have VGA arbitration disabled in the kernel. I am using a Radeon 7870 to passthrough to the guest, and this card did not have UEFI firmware available. I obtained the firmware file for this card online, maybe from manufacturer (can't remember), and modded it with UEFI portion of firmware from a newer R9 270. Using qemu romfile option with this modded file, I successfully passthrough this card to Windows guest booting with OVMF. I did not flash the modified firmware to the GPU itself, so I have to use the romfile in order for guest to boot with OVMF, although it is an option. _______________________________________________ vfio-users mailing list vfio-users@redhat.com https://www.redhat.com/mailman/listinfo/vfio-users
