linux-kernel - Re: [PATCH 07/13] pci: Provide sensible irq vector alloc/free routines

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:	Tue, 12 Jul 2016 14:46:03 +0200
From:	Alexander Gordeev <agordeev@...hat.com>
To:	Christoph Hellwig <hch@....de>
Cc:	tglx@...utronix.de, axboe@...com, linux-block@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-nvme@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/13] pci: Provide sensible irq vector alloc/free
 routines

On Tue, Jul 12, 2016 at 11:13:00AM +0200, Christoph Hellwig wrote:
> On Mon, Jul 11, 2016 at 12:43:41PM +0200, Alexander Gordeev wrote:
> > > I diagreed - if we deprecated functions the only thing that should
> > > be mentioned is a "don't use these". 
> > 
> > I will try to paraphrase myself. The new API deprecates pci_enable_msi*_range
> > functions, but I am not that sure about others. Certainly, pci_msi*_vec__ount
> > and pci_enable_msi*_exact could have (and AFAIR do have) uses that can not be
> > covered by automatic initialization of pci_alloc_irq_vectors().
> 
> pci_enable_msi*_exact is the equivalent of pci_enable_msi*_range
> with minvecs == maxvecs and treating any return value >= 0 as 0.

Right. And people asked explicitly to introduce these helpers when
range functions were introduced in the first place. Since there is
handful of drivers that do use pci_enable_msi*_exact() I suppose a
need for them persists.

> I've updated the documentation so that the old usage examples are kept
> around, but now use pci_alloc_irq_vectors.  I've also added a more detaild
> blurb on pci_msi*_vec_count - I think there is no need for them, but
> if I'm proven wrong we'll have to add a pci_irq_vector_count that handles
> all interrupt types later.

I guess, it is up to Bjorn. But.

Your proposed pci_nr_irq_vectors() function (a) is not a replacement for
pci_msi*_vec_count() and (b) would be useless if I read its description
properly:

(a) Functions pci_msi*_vec_count() return number of vectors reported by
a PCI device. It is a constant for the device and a driver may make an
assumption based on this number;

(b) A number returned by pci_nr_irq_vectors() is not guaranteed what a
following call to pci_alloc_irq_vectors() can return (since the number
of actually allocated vectors might change between the two calls).
Therefore, a value returned by pci_nr_irq_vectors() can not be used for
anything.