Re: [Qemu-devel] [RFC] Next gen kvm api

From: Scott Wood <scottwood@freescale.com>
To: Alexander Graf <agraf@suse.de>
Cc: Avi Kivity <avi@redhat.com>,
	Anthony Liguori <anthony@codemonkey.ws>,
	KVM list <kvm@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	qemu-devel <qemu-devel@nongnu.org>,
	kvm-ppc <kvm-ppc@vger.kernel.org>
Subject: Re: [Qemu-devel] [RFC] Next gen kvm api
Date: Fri, 17 Feb 2012 12:27:39 -0600	[thread overview]
Message-ID: <4F3E9C1B.5040404@freescale.com> (raw)
In-Reply-To: <016BCCE1-3E2C-4812-AA4D-2DC9D27CB457@suse.de>

On 02/16/2012 06:23 PM, Alexander Graf wrote:
> On 16.02.2012, at 21:41, Scott Wood wrote:
>> And yes, we do have fancier hardware coming fairly soon for which this
>> breaks (TLB0 entries can be loaded without host involvement, as long as
>> there's a translation from guest physical to physical in a separate
>> hardware table).  It'd be reasonable to ignore TLB0 for migration (treat
>> it as invalidated), but not for debug since that may be where the
>> translation we're interested in resides.
> 
> Could we maybe add an ioctl that forces kvm to read out the current tlb0 contents and push them to memory? How slow would that be?

Yes, I was thinking something like that.  We'd just have to remove (make
conditional on MMU type) the statement that this is synchronized
implicitly on return from vcpu_run.

Performance shouldn't be a problem -- we'd only need to sync once and
then can do all the repeated debug accesses we want.  So should be no
need to mess around with partial sync.

-Scott