Re: [PATCH] PCI: handle pci_sriov_set_totalvfs(dev, 0)

From: Edward Cree <ecree@solarflare.com>
To: Alexander Duyck <alexander.h.duyck@intel.com>
Cc: <linux-pci@vger.kernel.org>, Don Dutile <ddutile@redhat.com>,
	"Bjorn Helgaas" <bhelgaas@google.com>
Subject: Re: [PATCH] PCI: handle pci_sriov_set_totalvfs(dev, 0)
Date: Thu, 31 Jul 2014 16:56:58 +0100	[thread overview]
Message-ID: <53DA674A.9030305@solarflare.com> (raw)
In-Reply-To: <53DA5EF4.1030500@intel.com>

On 31/07/14 16:21, Alexander Duyck wrote:
> However if you are wanting to use this as a way to disable SR-IOV for a
> device I wouldn't recommend it.  Based on what you have described I
> would suggest dropping the fix in drivers/pci/quirks that would clear
> dev->is_physfn if you are in the PF-IOV mode.  That way the SR-IOV
> functionality should be fully disabled.
I still don't see how this can go in drivers/pci/quirks, because PF-IOV
mode can only be detected at driver probe time.  The way we find out
that the NIC is in PF-IOV mode is that a request to the MC (the
Management CPU on the card) to create a vswitch fails.  But maybe I'm
wrong about what quirks can do - is there any relevant documentation?

Clearing dev->is_physfn in the driver probe routine isn't safe:
dev->sriov memory can get leaked, for example, as sriov_init will get
called at device add, but sriov_release won't be called at removal.

I'm also unconvinced that having !(dev->is_physfn || dev->is_virtfn) is
a valid state; but maybe I'm misunderstanding and "is_physfn" doesn't
actually mean "is a physical function", but rather "has SR-IOV capability".
> In addition this solution would
> also resolve the fact that the driver wouldn't actually have to be
> loaded for it to work so if someone were to load a driver that didn't
> contain the fix they would be blocked from enabling SR-IOV as well.
The current driver fails to probe the PF because it assumes the vswitch
creation failure is fatal.  There should never be a driver that knows it
can live without the vswitch but doesn't know that that breaks SR-IOV.

-Edward
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