linux-kernel - Re: [PATCH] uio/uio_pci_generic: Add SR-IOV support

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Message-ID: <5c744ed0-2937-4460-fb8a-6e92fe5bfffa@redhat.com>
Date:   Mon, 2 Oct 2017 14:52:31 -0400
From:   Don Dutile <ddutile@...hat.com>
To:     David Woodhouse <dwmw2@...radead.org>,
        Alexander Duyck <alexander.duyck@...il.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        "Bryant G. Ly" <bryantly@...ux.vnet.ibm.com>,
        Bodong Wang <bodong@...lanox.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>, kvm@...r.kernel.org
Subject: Re: [PATCH] uio/uio_pci_generic: Add SR-IOV support

On 10/02/2017 08:35 AM, David Woodhouse wrote:
> On Thu, 2017-09-28 at 12:56 -0400, Don Dutile wrote:
>> Well, my point is more like: why put it in uio?
>> why not make it available via pcie, setup while/if no driver attached?
>> i.e., other non-uio users can use the mechanism.... like libvirt? ...
>> if a PF driver isn't required.
>
> This would allow you to enable SR-IOV on a PF before its driver is
> loaded, right? Even when that driver *is* going to need to perform
> resource management for those VFs?
>
> Would existing drivers cope with SR-IOV being enabled, and VFs being
> assigned to guests, before they're loaded? If so then sure, let's do it
> generically. But I'm not sure that's the case.
>
No better than a uio driver/mgmt api that may have to configure a PF
before a VF is enabled.
Q: So what is better: provide a common hook in sysfs for all to use,
    potentially causing a kernel fault (during vf probe/config), or
    a user-level program/mgmt-app that does the equivalent?

> As it is, the UIO driver is all about "userspace knows best". So if
> there's resource management to be done, then userspace needs to do that
> before enabling SR-IOV. And that's consistent with the current driver-
> based enabling model for SR-IOV.
>
I'm not seeing the UIO driver consistency here.  IMO, it's a similar
problem, moved to a different place. i.e., slightly different attack vector,
but same endpoint.