Subject: Re: [EXTERNAL] RE: [PATCH net] i40e/iavf: Fix msg interface between VF and PF

From: Arkady Gilinsky <[email-masked]>
Date: Wed, 6 Nov 2019 05:30:20 +0000

On Tue, 2019-11-05 at 16:55 +0000, Creeley, Brett wrote:
> > -----Original Message-----
> > From: Arkady Gilinsky <[email-masked]>
> > Sent: Monday, November 4, 2019 9:24 PM
> > To: Creeley, Brett <[email-masked]>; [email-masked]; [email-masked]; Kirsher,
> > Jeffrey T
> > <[email-masked]>
> > Cc: Arkady Gilinsky <[email-masked]>
> > Subject: Re: [EXTERNAL] RE: [PATCH net] i40e/iavf: Fix msg interface between VF and PF
> > > static bool i40e_vc_verify_vqs_bitmaps(struct virtchnl_queue_select *vqs)
> > > {
> > > 	/* this will catch any changes made to the virtchnl_queue_select bitmap */
> > > 	if (sizeof(vqs->rx_queues) != sizeof(u32) ||
> > > 	     sizeof(vqs->tx_queues) != sizeof(u32))
> > > 		return false;
> > 
> > If so, then is it better to check the type of the fields in compile-time rather than in runtime ?
> > Something like this:
> > BUILD_BUG_ON(sizeof(vqs->rx_queues) != sizeof(u32));
> > BUILD_BUG_ON(sizeof(vqs->tx_queues) != sizeof(u32));
> > This is not required comparison each time when function is called and made code more optimized.
> 
> I don't think this is required with the change you suggested below.
Agree.
If other code in driver not need to be adjusted/verified, then this check is not needed.
> 
> > > 
> > > 	if ((vqs->rx_queues == 0 && vqs->tx_queues == 0) ||
> > > 	      hweight32(vqs->rx_queues) > I40E_MAX_VF_QUEUES ||
> > > 	      hweight32(vqs->tx_queues) > I40E_MAX_VF_QUEUES)
> > > 		return false;
> > 
> > Again, from optimization POV it is better to have constant changed than variable,
> > since it is compile time and not run time action:
> > 	if ((vqs->rx_queues == 0 && vqs->tx_queues == 0) ||
> > 	      vqs->rx_queues >= (BIT(I40E_MAX_VF_QUEUES)) ||
> > 
> >       vqs->tx_queues >= (BIT(I40E_MAX_VF_QUEUES)))
> > 		return false;
> 
> This seems much better than my solution. It fixes the original issue, handles if the
> vqs->[r|t]x_queues variables have changed in size, and the queue bitmap comparison
> uses a constant. Thanks!
Thanks to you for feedback.
I am trying to understand if this patch will enter into official kernel tree
and, not less important from my POV, to official Intel drivers.
Brett/Jeffrey, could you, please, assist to make sure that this fix, or fix suggested by Brett,
will be integrated into Intel i40e/iavf drivers ?
Or may be I should write mail straight to Intel support ?
> > > 	return true;
> > > }
-- 
Best regards,
Arkady Gilinsky

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