linux-kernel - Re: [PATCH 1/3] PCI/MSI: Add pci_enable_msi

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Date:	Fri, 4 Jul 2014 11:54:34 +0200
From:	Alexander Gordeev <agordeev@...hat.com>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	"'Bjorn Helgaas'" <bhelgaas@...gle.com>,
	"linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>,
	"linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 1/3] PCI/MSI: Add pci_enable_msi_partial()

On Fri, Jul 04, 2014 at 09:11:50AM +0000, David Laight wrote:
> > I might be missing something, but we are talking of MSI address space
> > here, aren't we? I am not getting how we could end up with a 'write'
> > to a random kernel location when a unclaimed MSI vector sent. We could
> > only expect a spurious interrupt at worst, which is handled and reported.
> > 
> > Anyway, as I described in my reply to Bjorn, this is not a concern IMO.
> 
> I'm thinking of the following - which might be MSI-X ?
> 1) Hardware requests some interrupts and tells the host the BAR (and offset)
>    where the 'vectors' should be written.
> 2) To raise an interrupt the hardware uses the 'vector' as the address
>    of a normal PCIe write cycle.
> 
> So if the hardware requests 4 interrupts, but the driver (believing it
> will only use 3) only write 3 vectors, and then the hardware uses the
> 4th vector it can write to a random location.
> 
> Debugging that would be hard!

MSI base address is kind of hardcoded for a platform. A combination of
MSI base address, PCI function number and MSI vector makes a PCI host to
raise interrupt on a CPU. I might be inaccurate in details, but the scenario
you described is impossible AFAICT.

> 	David
> 
> 
> 

-- 
Regards,
Alexander Gordeev
agordeev@...hat.com
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