linux-kernel - Re: [RFC] /dev/ioasid uAPI proposal

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Date:   Wed, 9 Jun 2021 11:32:35 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        Robin Murphy <robin.murphy@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        David Gibson <david@...son.dropbear.id.au>,
        Kirti Wankhede <kwankhede@...dia.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Jason Wang <jasowang@...hat.com>
Subject: Re: [RFC] /dev/ioasid uAPI proposal

On Wed, Jun 09, 2021 at 03:24:11PM +0200, Paolo Bonzini wrote:
> On 09/06/21 14:47, Jason Gunthorpe wrote:
> > On Wed, Jun 09, 2021 at 02:46:05PM +0200, Paolo Bonzini wrote:
> > > On 09/06/21 13:57, Jason Gunthorpe wrote:
> > > > On Wed, Jun 09, 2021 at 02:49:32AM +0000, Tian, Kevin wrote:
> > > > 
> > > > > Last unclosed open. Jason, you dislike symbol_get in this contract per
> > > > > earlier comment. As Alex explained, looks it's more about module
> > > > > dependency which is orthogonal to how this contract is designed. What
> > > > > is your opinion now?
> > > > 
> > > > Generally when you see symbol_get like this it suggests something is
> > > > wrong in the layering..
> > > > 
> > > > Why shouldn't kvm have a normal module dependency on drivers/iommu?
> > > 
> > > It allows KVM to load even if there's an "install /bin/false" for vfio
> > > (typically used together with the blacklist directive) in modprobe.conf.
> > > This rationale should apply to iommu as well.
> > 
> > I can vaugely understand this rational for vfio, but not at all for
> > the platform's iommu driver, sorry.
> 
> Sorry, should apply to ioasid, not iommu (assuming that /dev/ioasid support
> would be modular).

/dev/ioasid and drivers/iommu are tightly coupled things, I we can put
a key symbol or two in a place where it will not be a problem to
depend on.

Jason