Re: [Xen-users] xen 4.4 errors and misunderstanding

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Sun, 2015-05-10 at 11:43 +0300, darkshvein l wrote:
> Good day, people.
> 
> I run windows on xen 4.4. 
> 
> After decreasing RAM from 9 to 3 Gb it was works.
> 
> But, I met another problem
> 
> 
> 
> >libxl: error: libxl_pci.c:990:libxl__device_pci_reset: The kernel
> doesn't support reset from sysfs for PCI device 0000:01:00.0
> 
> 
> 0000:01:00.0 - radeon 7850, xen 4.1 all fine.
> 
> 1.where/what is this kernel reset option? 

Resetting a PCI device should be simple, after all there are more or
less standardized ways of doing so. However in reality many devices do
not implement these interfaces or implement customise or quirky ones.

So Xen relies on the kernel (which has drivers for the PCI bus and often
the specific hardware device) to know all this and to present a reset
method to userspace (via sysfs). However the kernel cannot always do
this (i..e if it lacks a quirk for a given device).

If a device cannot be reset prior to passthrough then it may not be
completely quiesced, which can cause strange behaviour.

In practice it seems to often be the case that it is ok to passthrough
without resetting, especially if you have configured pciback such that
the device is never actively used by dom0 before you pass it to the
guest.

> 2. what about memory barrier?

What about them?

Ian.



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