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

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Message-ID: <20090828194825.GM4884@parisc-linux.org>
Date:	Fri, 28 Aug 2009 13:48:26 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	Chris Wright <chrisw@...s-sol.org>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	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

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.

Yes, I think that would be preferable.  We have a *LOT* of resources in
the kernel, and the embedded folks would not find it funny if they all
grew in size suddenly.

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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