netdev - RE: [PATCH iwl-next] ice: store VF's pci_dev ptr in ice

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Date: Tue, 22 Aug 2023 20:46:46 +0000
From: "Keller, Jacob E" <jacob.e.keller@...el.com>
To: Leon Romanovsky <leon@...nel.org>, "Kitszel, Przemyslaw"
	<przemyslaw.kitszel@...el.com>
CC: "Nguyen, Anthony L" <anthony.l.nguyen@...el.com>, "Brandeburg, Jesse"
	<jesse.brandeburg@...el.com>, "intel-wired-lan@...ts.osuosl.org"
	<intel-wired-lan@...ts.osuosl.org>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>, "Polchlopek, Mateusz"
	<mateusz.polchlopek@...el.com>
Subject: RE: [PATCH iwl-next] ice: store VF's pci_dev ptr in ice_vf



> -----Original Message-----
> From: Leon Romanovsky <leon@...nel.org>
> Sent: Monday, August 21, 2023 4:02 AM
> To: Kitszel, Przemyslaw <przemyslaw.kitszel@...el.com>
> Cc: Nguyen, Anthony L <anthony.l.nguyen@...el.com>; Brandeburg, Jesse
> <jesse.brandeburg@...el.com>; intel-wired-lan@...ts.osuosl.org;
> netdev@...r.kernel.org; Polchlopek, Mateusz <mateusz.polchlopek@...el.com>;
> Keller, Jacob E <jacob.e.keller@...el.com>
> Subject: Re: [PATCH iwl-next] ice: store VF's pci_dev ptr in ice_vf
> 
> On Mon, Aug 21, 2023 at 12:48:40PM +0200, Przemek Kitszel wrote:
> > On 8/18/23 20:20, Leon Romanovsky wrote:
> > > On Fri, Aug 18, 2023 at 02:20:51PM +0200, Przemek Kitszel wrote:
> > > > On 8/16/23 16:31, Leon Romanovsky wrote:
> > > > > On Wed, Aug 16, 2023 at 04:54:54AM -0400, Przemek Kitszel wrote:
> > > > > > Extend struct ice_vf by vfdev.
> > > > > > Calculation of vfdev falls more nicely into ice_create_vf_entries().
> > > > > >
> > > > > > Caching of vfdev enables simplification of
> ice_restore_all_vfs_msi_state().
> > > > >
> > > > > I see that old code had access to pci_dev * of VF without any locking
> > > > > from concurrent PCI core access. How is it protected? How do you make
> > > > > sure that vfdev is valid?
> > > > >
> > > > > Generally speaking, it is rarely good idea to cache VF pci_dev pointers
> > > > > inside driver.
> > > > >
> > > > > Thanks
> > > >
> > > > Overall, I do agree that ice driver, as a whole, has room for improvement in
> > > > terms of synchronization, objects lifetime, and similar.
> > > >
> > > > In this particular case, I don't see any reason of PCI reconfiguration
> > > > during VF lifetime, but likely I'm missing something?
> > >
> > > You are caching VF pointer in PF,
> >
> > that's correct that the driver is PF/ice
> >
> > > and you are subjected to PF lifetime
> > > and not VF lifetime.
> >
> > this belongs to struct ice_vf, which should have VF lifetime,
> > otherwise it's already at risk
> 
> I'm not so sure about it. ICE used to use devm_* API and not explicit
> kalloc/kfree calls, it is not clear anymore the lifetime scope of VF
> structure.
> 
> Thanks
> 

The ice_vf structure is now reference counted with a kref, and is created when VFs are added, and removed when the VF is removed.

Thanks,
Jake