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Re: [PATCH v2 0/3] exclude hyperv synic sections from vhost

From: Dr. David Alan Gilbert
Subject: Re: [PATCH v2 0/3] exclude hyperv synic sections from vhost
Date: Fri, 17 Jan 2020 12:35:04 +0000
User-agent: Mutt/1.13.0 (2019-11-30)

* Paolo Bonzini (address@hidden) wrote:
> On 13/01/20 18:36, Dr. David Alan Gilbert (git) wrote:
> > 
> > Hyperv's synic (that we emulate) is a feature that allows the guest
> > to place some magic (4k) pages of RAM anywhere it likes in GPA.
> > This confuses vhost's RAM section merging when these pages
> > land over the top of hugepages.
> Can you explain what is the confusion like?  The memory API should just
> tell vhost to treat it as three sections (RAM before synIC, synIC
> region, RAM after synIC) and it's not clear to me why postcopy breaks
> either.

See my v3 I posted yesterday; I've made this a lot simpler by just
turning the alignment off for vhost-kernel and only enabling it for
vhost-user;  vhost-user skips any section without a backing fd anyway,
so the synic problem goes away, as does another problem reported by
Peter Lieven that he was seeing that seemed like one of the VGA regions
getting in the way (which I'd not seen before).


> Paolo
> > Since they're not normal RAM, and they shouldn't have vhost DMAing
> > into them, exclude them from the vhost set.
Dr. David Alan Gilbert / address@hidden / Manchester, UK

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