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Re: [PATCH for-5.0 v11 08/20] virtio-iommu: Implement translate

From: Jean-Philippe Brucker
Subject: Re: [PATCH for-5.0 v11 08/20] virtio-iommu: Implement translate
Date: Thu, 9 Jan 2020 12:15:44 +0100

On Thu, Jan 09, 2020 at 12:01:26PM +0100, Auger Eric wrote:
> Hi,
> On 1/9/20 11:40 AM, Jean-Philippe Brucker wrote:
> > On Thu, Jan 09, 2020 at 09:58:49AM +0100, Auger Eric wrote:
> >>>> I share Peter's concern about having a different default policy than x86.
> >>>
> >>> Yes I'd say just align with whatever policy is already in place. Do you
> >>> think we could add a command-line option to let people disable
> >>> default-bypass, though?  That would be a convenient way to make the IOMMU
> >>> protection airtight for those who need it.
> >> Yes I could easily add a device option to disable the default bypass.
> >>
> >> Shall we change the meaning of the F_BYPASS feature then? If exposed by
> >> the device, the device does bypass by default, otherwise it doesn't.
> >> This would be controlled by the device option.
> > 
> > For a device that doesn't do bypass by default, the driver wouldn't have
> > the ability to enable bypass (feature bit not offered, not negotiable).
> > 
> >> The driver then could have means to overwrite this behavior once loaded?
> > 
> > Let's keep the bypass feature bit for this. If the bit is offered, the
> > driver chooses to enable or disable it. If the bit is not offered or not
> > negotiated, then the behavior is deny. If the bit is offered and
> > negotiated then the behavior is allow.
> > 
> > We can say that before features negotiation (latched at features register
> > write, I think, in practice?) the behavior is platform dependent. The
> > current wording about bypass intends to discourage unsafe choices but
> > makes a strong statement only about the device behavior after features
> > negotiation. 
> OK. May be worth adding in the spec later.
> By the way what is the plan for the vote?

The ballot closed and the spec is accepted for virtio-v1.2-cs01, with the
condition that the stale statement about padding is removed


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