linux-kernel - Re: [PATCH] Enable SR-IOV instantiation through /sys file

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Date:   Mon, 6 Nov 2017 16:27:13 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     "Wang, Liang-min" <liang-min.wang@...el.com>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Duyck, Alexander H" <alexander.h.duyck@...el.com>,
        "O'riordain, Seosamh" <seosamh.oriordain@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [PATCH] Enable SR-IOV instantiation through /sys file

On Tue, 31 Oct 2017 12:55:20 +0000
"Wang, Liang-min" <liang-min.wang@...el.com> wrote:

> > -----Original Message-----
> > From: David Woodhouse [mailto:dwmw2@...radead.org]
> > Sent: Monday, October 30, 2017 8:39 AM
> > To: Christoph Hellwig <hch@...radead.org>; Duyck, Alexander H
> > <alexander.h.duyck@...el.com>
> > Cc: Wang, Liang-min <liang-min.wang@...el.com>;
> > alex.williamson@...hat.com; linux-kernel@...r.kernel.org; Kirsher, Jeffrey T
> > <jeffrey.t.kirsher@...el.com>; kvm@...r.kernel.org; bhelgaas@...gle.com;
> > linux-pci@...r.kernel.org
> > Subject: Re: [PATCH] Enable SR-IOV instantiation through /sys file
> > 
> > On Sat, 2017-10-28 at 23:16 -0700, Christoph Hellwig wrote:  
> > > On Fri, Oct 27, 2017 at 11:20:41PM +0000, Duyck, Alexander H wrote:  
> > > >
> > > > I don't see this so much as a security problem per-se. It all depends
> > > > on the hardware setup. If I recall correctly, there are devices where
> > > > the PF function doesn't really do much other than act as a bit more
> > > > heavy-weight VF, and the actual logic is handled by a firmware engine
> > > > on the device.  
> > >
> > > Can you cite an example?  While those surely could exist in theory,
> > > I can't think of a practical example.  
> > 
> > I have them, which is why I'm patching the UIO driver to allow num_vfs
> > to be set. I don't even want to *use* the UIO driver for any purpose
> > except to make that appear in sysfs. It's all handled in the device.
> > 
> > (I think we might be able to just give the PF out to a guest as if it
> > were just another VF, but I don't think we actually *do* that right
> > now).  
> 
> Under UEFI secure boot environment, kernel puts restrictions on UIO and its derivatives.
> So, user-space function/driver based upon UIO is no longer working under UEFI secure
> boot environment. The next viable option is vfio-pci, hence this patch in parallel with
> UIO work.

If you want a PF driver that does nothing other than allow SR-IOV to be
enabled, doesn't that scream pci-stub?  Trying to overlay it onto a
driver that also allows userspace driver access to that device seems
like the worst idea.  Thanks,

Alex