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A question about IOMMU
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pirilli View Drop Down
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Joined: 21 Nov 2020
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Points: 254 		Post Options Post Options   Thanks (0) Thanks(0)   Quote pirilli Quote  Post ReplyReply Direct Link To This Post Topic: A question about IOMMU
    Posted: 21 Nov 2020 at 2:43pm
Good morning.
I'm on a B450M PRO-4-f Asrock. CPu is ryzen 3100.
I have two cards, one is AMD Radeon hd, another one is Nvidia GT710.
The first card is in the second slot, and is the main card.
The second card is in the last slot, and I want to pass it via pci passtrough
to a Windows guest, host system is Linux Slackware Current.
There is only one problem..the ATI card (used on host) is in the iommu group 16
and the nvidia is in the group 15, as you can see from this output there is a lot of devices on group 15, so if i want to use the windows guest i have to pass it a lot of devices and this is impossible(i have to pass the ethernet card too!).


IOMMU Group 15 01:00.2 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] 400 Series Chipset PCIe Bridge [1022:43c6] (rev 01)
IOMMU Group 15 02:00.0 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] 400 Series Chipset PCIe Port [1022:43c7] (rev 01)
IOMMU Group 15 02:01.0 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] 400 Series Chipset PCIe Port [1022:43c7] (rev 01)
IOMMU Group 15 02:04.0 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] 400 Series Chipset PCIe Port [1022:43c7] (rev 01)
IOMMU Group 15 04:00.0 Ethernet controller [0200]: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller [10ec:8168] (rev 11)
IOMMU Group 15 05:00.0 VGA compatible controller [0300]: NVIDIA Corporation GK208B [GeForce GT 710] [10de:128b] (rev a1)
IOMMU Group 15 05:00.1 Audio device [0403]: NVIDIA Corporation GK208 HDMI/DP Audio Controller [10de:0e0f] (rev a1)
IOMMU Group 16 06:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] Cedar [Radeon HD 5000/6000/7350/8350 Series] [1002:68f9]
IOMMU Group 16 06:00.1 Audio device [0403]: Advanced Micro Devices, Inc. [AMD/ATI] Cedar HDMI Audio [Radeon HD 5400/6300/7300 Series] [1002:aa68]


An easy solution can be: use a new cpu(sic!) with integrated gpu but i have bought recently this 3100 without gpu and I cannot spent other money for another cpu.
A better solution was: use the card in iommu group 15(change ati with nvidia, or using nvidia as host card and pass ati ) but I cannot found on the bios the setting of primary device to use for output, I don't know also if is possible or not.
Someone can help, any suggestion?
Thanks
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tychondus View Drop Down
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Joined: 14 Dec 2020
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Points: 1 		Post Options Post Options   Thanks (0) Thanks(0)   Quote tychondus Quote  Post ReplyReply Direct Link To This Post Posted: 14 Dec 2020 at 1:55pm
Kinda late. But you could try the ACS override patch. Im assuming you are using linux. You are going to have to do your own homework on this. Arch has a some info on this in their wiki: https://wiki.archlinux.org/index.php/PCI_passthrough_via_OVMF#Bypassing_the_IOMMU_groups_.28ACS_override_patch.29
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pirilli View Drop Down
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Points: 254 		Post Options Post Options   Thanks (0) Thanks(0)   Quote pirilli Quote  Post ReplyReply Direct Link To This Post Posted: 15 Dec 2020 at 5:07am
Yes I'm on Linux, but i don't trust acs patch, can made system unstable.
I have found a "workaround", using single card vga passtrough.
I did this 


telinit 3  #X11 must not run
login...
pulseaudio -D
virsh start windowsvm #with the same vga of host passed


Works fine all, only one problem.
The card fall "asleep" after guest shutdown, and I had to reboot using ctrl+alt+canc or shutdown cleanly with button power(is possible, only need acpid demon active. Or ssh to host and shutdown -r now.
Thanks for answer
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