linux-kernel - Re: [PATCH v3 2/3] vfio/pci: Tolerate oversized BARs by disallowing mmap

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Date: Wed, 19 Jun 2024 00:11:52 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Alex Williamson <alex.williamson@...hat.com>
Cc: Niklas Schnelle <schnelle@...ux.ibm.com>,
	Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>,
	Gerd Bayer <gbayer@...ux.ibm.com>,
	Matthew Rosato <mjrosato@...ux.ibm.com>,
	Jason Gunthorpe <jgg@...pe.ca>, linux-s390@...r.kernel.org,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v3 2/3] vfio/pci: Tolerate oversized BARs by disallowing
 mmap

On Tue, Jun 18, 2024 at 09:51:34AM -0600, Alex Williamson wrote:
> > -		if (!resource_size(res))
> > +		if (!resource_size(res) ||
> > +		    resource_size(res) > (IOREMAP_END + 1 - IOREMAP_START))
> >  			goto no_mmap;
> >  
> >  		if (resource_size(res) >= PAGE_SIZE) {
> > 
> 
> A powerpc build reports:
> 
> ERROR: modpost: "__kernel_io_end" [drivers/vfio/pci/vfio-pci-core.ko] undefined!
> 
> Looks like only __kernel_io_start is exported.  Thanks,

And exported code has no business looking at either one.

I think the right thing here is a core PCI quirk to fix the BAR
size of the ISM device instead of this hack in vfio.