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Re: [Qemu-devel] [PATCH 5/5] intel_iommu: turn on IR by default

From: Peter Xu
Subject: Re: [Qemu-devel] [PATCH 5/5] intel_iommu: turn on IR by default
Date: Wed, 19 Dec 2018 13:21:40 +0800
User-agent: Mutt/1.10.1 (2018-07-13)

On Tue, Dec 18, 2018 at 01:30:23PM +0100, Paolo Bonzini wrote:
> On 18/12/18 04:07, Peter Xu wrote:
> > On Mon, Dec 17, 2018 at 03:31:14PM +0800, Peter Xu wrote:
> >> IR has been there for a long time and long time no bug reported.
> >> Let's turn it on by default to match general hardwares.  Providing
> >> compatibility bit for QEMU<=3.1.
> >>
> >> Signed-off-by: Peter Xu <address@hidden>
> > I forgot that IR will depend on split kernel irqchip and by default
> > that's still "on" so "-M q35 -device intel-iommu" may not be able to
> > boot correctly with all the default values and instead QEMU will ask
> > user to turn on split irqchip.
> > 
> > Paolo/Michael, do you think it would make any sense to turn the
> > default kernel-irqchip machine parameter to split starting from qemu
> > 4.0?  Since AFAIU it should have little degradation to performance but
> > at the same time it reduces kvm attack serface, which seems good.
> The main problem with that would be the minimal required kernel version,
> which is 4.4 for split irqchip.  But, we're already planning to make it
> 4.5 so it's not an issue.  Go for it. :)

Thanks Paolo. :)

I'll try to prepare a patch for it.


Peter Xu

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