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rabcor
Apprentice
Joined: 05 Apr 2012
Posts: 200
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 Posted: Sun Jun 01, 2014 1:26 pm Post subject: Permission problem with vfio-pci |
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I am trying to run a qemu virtual machine with a VGA Passthrough setup.
In short, I enabled pci-stub to claim my graphics card on boot, then using the kernel "vfio-pci" module I run the following script
| Code: | #!/bin/bash
modprobe vfio-pci
for dev in "$@"; do
vendor=$(cat /sys/bus/pci/devices/$dev/vendor)
device=$(cat /sys/bus/pci/devices/$dev/device)
if [ -e /sys/bus/pci/devices/$dev/driver ]; then
echo $dev > /sys/bus/pci/devices/$dev/driver/unbind
fi
echo $vendor $device > /sys/bus/pci/drivers/vfio-pci/new_id
done |
To bind the GPU to vfio. Then I launch qemu with these commands to bind the card to my VM:
| Code: | | -device vfio-pci,host=02:00.0,bus=root.1,addr=00.0,multifunction=on,x-vga=on -device vfio-pci,host=02:00.1,bus=root.1,addr=00.1 |
It executes just fine as root, but if I run it as a user it fails and gives me a permission error:
| Code: | qemu-system-x86_64: -device vfio-pci,host=02:00.0,bus=root.1,addr=00.0,multifunction=on,x-vga=on: vfio: error opening /dev/vfio/13: Permission denied
qemu-system-x86_64: -device vfio-pci,host=02:00.0,bus=root.1,addr=00.0,multifunction=on,x-vga=on: vfio: failed to get group 13
qemu-system-x86_64: -device vfio-pci,host=02:00.0,bus=root.1,addr=00.0,multifunction=on,x-vga=on: Device initialization failed.
qemu-system-x86_64: -device vfio-pci,host=02:00.0,bus=root.1,addr=00.0,multifunction=on,x-vga=on: Device 'vfio-pci' could not be initialized
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For more info here are my groups:
| Code: | $ groups
disk wheel audio video kvm users plugdev rabcor
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What would you think is the safest way to solve that? (Running a VM as root is not something I would consider safe)
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This picture was my biggest reason for ever trying Gentoo <3 |
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khayyam
Watchman
Joined: 07 Jun 2012
Posts: 6227
Location: Room 101
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| Posted: Sun Jun 01, 2014 2:20 pm Post subject: Re: Permission problem with vfio-pci |
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rabcor ... I can't answer your specific problem, but I'd suggest the following improvements to your script:
| Code: | #!/bin/sh
modprobe vfio-pci
for dev in "$@"; do
read -r vendor </sys/bus/pci/devices/$dev/vendor
read -r device </sys/bus/pci/devices/$dev/device
if [ -e /sys/bus/pci/devices/$dev/driver ]; then
echo $dev > /sys/bus/pci/devices/$dev/driver/unbind
fi
echo $vendor $device > /sys/bus/pci/drivers/vfio-pci/new_id
done |
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rabcor
Apprentice
Joined: 05 Apr 2012
Posts: 200
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| Posted: Sun Jun 01, 2014 3:36 pm Post subject: |
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Thanks  I have no idea how that's an improvement though, isn't it just a different way to achieve the same result?
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This picture was my biggest reason for ever trying Gentoo <3 |
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khayyam
Watchman
Joined: 07 Jun 2012
Posts: 6227
Location: Room 101
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| Posted: Sun Jun 01, 2014 6:34 pm Post subject: |
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| rabcor wrote: | | Thanks 8) I have no idea how that's an improvement though, isn't it just a different way to achieve the same result? |
rabcor ... you're welcome ... well, yes, it achieves the same result, but 'read' is a shell builtin whereas 'cat' isn't (so, a UUoC).
The reason we have various shell builtins is to make tasks like the above easy, and so that rather than call an external command, we can use the shell itself (which, generally, will make our code less resource intensive).
best ... khay |
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