Re: Any pv shim examples ???

[Brad Spencer <brad%anduin.eldar.org@localhost>]

Manuel Bouyer <bouyer%antioche.eu.org@localhost> writes:

> On Fri, Jul 08, 2022 at 07:17:42PM -0400, Brad Spencer wrote:
>> 
>> So, I noticed that there is a message in the Xen 4.15.2 package
>> mentioning that 32 bit PV guests will need to use pv shim in the future
>> as direct support is going away.  I attempted to use that with a very
>> old NetBSD 8.x 32 bit PV test guest I have on a NetBSD 9.2 DOM0 and it
>> didn't work.  I do not quite understand how pv shim works, but it
>> appears to want to start something like another DOM0 and that crashes.
>> 
>> Just wondering if anyone has had this work for them.
>
> yes, it works for me, with 4.15.2 and 4.15.3. Just add
> type=pvh
> pvshim=1
>
> to your config file.
>
> Basically pvshim emulates the PV MMU hypercalls in a PVH environnement


Thanks for verifying that..  I tried the above and it didn't work, but I
think I know why.  The pv shim feature uses pvh, as you mentioned, but
pvh requires a IOMMU and the system I tried it on doesn't have one.  It
does have SVM support, so HVM guests are pretty happy, but the
motherboard or BIOS doesn't seem to support enabling any IOMMU.  The
processor I have should support a IOMMU, but it can't be turned on it
seems.  The guest crashes when I try using pv shim in a manor that
doesn't make it clear that the IOMMU is required, assuming that is the
problem.  I wasn't sure if there was DOM0 NetBSD version requirements
for getting pv shim working.



Thanks...

-- 
Brad Spencer - brad%anduin.eldar.org@localhost - KC8VKS - http://anduin.eldar.org