linux-kernel - Re: [PATCH 3/5] vhost: support upto 509 memory regions

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Date:	Fri, 19 Jun 2015 18:26:27 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Igor Mammedov <imammedo@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, andrey@...l.ru
Subject: Re: [PATCH 3/5] vhost: support upto 509 memory regions

On 19/06/2015 18:20, Michael S. Tsirkin wrote:
> > We could, but I/O is just an example.  It can be I/O, a network ring,
> > whatever.  We cannot audit all address_space_map uses.
> > 
>
> No need to audit them all: defer device_add using an hva range until
> address_space_unmap drops using hvas in range drops reference count to
> 0.

That could be forever.  You certainly don't want to lockup the monitor
forever just because a device model isn't too friendly to memory hot-unplug.

That's why you need to audit them (also, it's perfectly in the device
model's right to use address_space_unmap this way: it's the guest that's
buggy and leaves a dangling reference to a region before unplugging it).

Paolo
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