linux-kernel - Re: [PATCH] SR-IOV: correct broken resource alignment calculations

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Message-ID: <20090828195823.GJ10360@sequoia.sous-sol.org>
Date:	Fri, 28 Aug 2009 12:58:23 -0700
From:	Chris Wright <chrisw@...s-sol.org>
To:	Greg KH <greg@...ah.com>
Cc:	Chris Wright <chrisw@...s-sol.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	Matthew Wilcox <matthew@....cx>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Yu Zhao <yu.zhao@...el.com>, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, stable@...nel.org
Subject: Re: [PATCH] SR-IOV: correct broken resource alignment calculations

* Greg KH (greg@...ah.com) wrote:
> On Fri, Aug 28, 2009 at 12:17:14PM -0700, Chris Wright wrote:
> > An SR-IOV capable device includes an SR-IOV PCIe capability which
> > describes the Virtual Function (VF) BAR requirements.  A typical SR-IOV
> > device can support multiple VFs whose BARs must be in a contiguous region,
> > effectively an array of VF BARs.  The BAR reports the size requirement
> > for a single VF.  We calculate the full range needed by simply multiplying
> > the VF BAR size with the number of possible VFs and create a resource
> > spanning the full range.
> > 
> > This all seems sane enough except it artificially inflates the alignment
> > requirement for the VF BAR.  The VF BAR need only be aligned to the size
> > of a single BAR not the contiguous range of VF BARs.  This can cause us
> > to fail to allocate resources for the BAR despite the fact that we
> > actually have enough space.
> > 
> > This patch adds a support for a new resource alignment type,
> > IORESOURCE_VSIZEALIGN, and allows struct resource to keep track of the
> > size requirements of a VF BAR which are smaller than the full resource
> > size.  This could also be done all within the PCI layer w/out bloating
> > struct resource or using the last available bit for alignment types.
> > 
> > Comments?
> > 
> > Signed-off-by: Chris Wright <chrisw@...s-sol.org>
> > Cc: Jesse Barnes <jbarnes@...tuousgeek.org>
> > Cc: Ivan Kokshaysky <ink@...assic.park.msu.ru>
> > Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> > Cc: Matthew Wilcox <matthew@....cx>
> > Cc: Yu Zhao <yu.zhao@...el.com>
> > Cc: stable@...nel.org
> 
> This is a new feature, which seems to be odd to have it sent to stable
> :)

Yeah, it's broken now (and shipped in 2.6.30).

> Does this fix reported problems in the "wild"?


Depending on card firwmware, yeah, I've hit this problem.


thanks,
-chris
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