netdev - Re: [PATCH mlx5-next v1 2/5] PCI: Add SR-IOV sysfs entry to read number of MSI-X vectors

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Date:   Fri, 15 Jan 2021 10:06:19 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
CC:     Alex Williamson <alex.williamson@...hat.com>,
        Leon Romanovsky <leon@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Jakub Kicinski <kuba@...nel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        <linux-rdma@...r.kernel.org>, Netdev <netdev@...r.kernel.org>,
        Don Dutile <ddutile@...hat.com>
Subject: Re: [PATCH mlx5-next v1 2/5] PCI: Add SR-IOV sysfs entry to read
 number of MSI-X vectors

On Thu, Jan 14, 2021 at 05:56:20PM -0800, Alexander Duyck wrote:

> That said, it only works at the driver level. So if the firmware is
> the one that is having to do this it also occured to me that if this
> update happened on FLR that would probably be preferred. 

FLR is not free, I'd prefer not to require it just for some
philosophical reason.

> Since the mlx5 already supports devlink I don't see any reason why the
> driver couldn't be extended to also support the devlink resource
> interface and apply it to interrupts.

So you are OK with the PF changing the VF as long as it is devlink not
sysfs? Seems rather arbitary?

Leon knows best, but if I recall devlink becomes wonky when the VF
driver doesn't provide a devlink instance. How does it do reload of a
VF then?

I think you end up with essentially the same logic as presented here
with sysfs.

> > It is possible for vfio to fake the MSI-X capability and limit what a
> > user can access, but I don't think that's what is being done here.
> 
> Yeah, I am assuming that is what is being done here. 

Just to be really clear, that assumption is wrong

Jason