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Re: [Qemu-discuss] How to resolve "Failed to mmap" error?

From: Alex Williamson
Subject: Re: [Qemu-discuss] How to resolve "Failed to mmap" error?
Date: Wed, 5 Oct 2016 10:33:32 -0600

On Wed, 5 Oct 2016 02:13:21 -0700
A223 A223 <address@hidden> wrote:

> Hello,
> When attempting PCI passthrough of a USB controller using the
> following parameter to qemu:
> -device vfio-pci,host=05:00.0,bus=root.1,addr=00.5
> I receive the following error:
> qemu-system-x86_64: -device
> vfio-pci,host=05:00.0,bus=root.1,addr=00.5: Failed to mmap
> 0000:05:00.0 BAR 2. Performance may be slow
> Ultimately, the controller does somewhat work in the VM, but I am
> suffering some performance and reliability issues with it, so I
> suspect this error message is pointing to the issue.
> How can I go about tracking down the root cause of this error?

This often means that the device resources are in use by another,
non-pci driver.  Look in /proc/iomem and /proc/ioport to see if any
drivers are claiming sub-regions on the device.  You can also turn on
tracing and look for the event vfio_region_mmap_fault, which might give
us more information (see docs/tracing.txt).  Also, please provide 'sudo
lspci -vvvs 5:00.0' so we can see the device resources.  Thanks,


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