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Re: [vfio-users] 1 GB hugepages cause host crash on guest shutdown with some GPUs

On December 5, 2015 at 20:38:17, Hristo Iliev (hristo hiliev eu) wrote:
Hi Okky, 

Just to add another data point. My system is also Haswell-E (i7-5820K on an 
X99 motherboard) and my Win10 VM does not make it past the OVMF spash screen 
with the symptomatic 100% CPU usage when the host is running linux-lts, but 
boots flawlessly on linux-vfio-lts. 

Hi Hristo,

Actually the 100% CPU usage issue reside on the changes on the kernel linux starting 4.2.x and the implementation of OVMF. Since the latest linux-vfio is based on linux 4.2.x, the issue also reside on that kernel. There’s a patch [1] for linux 4.3-mainline if you want to upgrade your kernel, I’ve tried it out myself on Z87 platform, but I haven’t found a patch for linux 4.2.x. If you want stableness, linux-lts-4.1.13 seems the latest stable right now.

I just upgraded my rig to a Haswell-E platform (Intel Core i7-5820K also, plus ASUS X99-A) last weekend, and I found no issues running pure linux-lts-4.1.13 (even the config is from lts). Though, I recompiled the kernel again with ABS and native CFLAGS hoping to have even better performance. Are you sure you meant linux-lts not linux-vfio (4.2.x)?

Oddly enough, sometimes the VM seems to be able to boot on linux-lts too, 
but only once it was successfully booted on the vfio-patched kernel. Could 
have something to do with some sort of initialisation of the GPU I'm passing 
through (GTX 970), which is able to survive host reboots. I'm using OVMF 
from the RPMs linked on the Arch Wiki and updating it regularly. 

Hmm, that’s weird. Haswell-E platform should not need any PCIe ACS workaround patch. Its IOMMU groups are separated nicely for each device. Can you try using linux-vfio-lts’ config and recompile linux-lts using the config with ABS and try booting the guest again? 

I would really prefer to use linux-lts instead of waiting for the newest 
linux-vfio-lts to finish compiling each time it gets updated, but that 
doesn't seem currently possible. 

Recompiling on your machine probably just took around 10 minutes actually. :D


[1] http://www.spinics.net/lists/kvm/msg123325.html

Okky Hendriansyah

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