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

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Date: Wed, 22 May 2024 20:19:35 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Niklas Schnelle <schnelle@...ux.ibm.com>
Cc: 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>,
	Alex Williamson <alex.williamson@...hat.com>,
	Gerd Bayer <gbayer@...ux.ibm.com>,
	Matthew Rosato <mjrosato@...ux.ibm.com>, linux-s390@...r.kernel.org,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH 2/3] vfio/pci: Tolerate oversized BARs by disallowing mmap

On Tue, May 21, 2024 at 02:14:58PM +0200, Niklas Schnelle wrote:
> On s390 there is a virtual PCI device called ISM which has a few rather
> annoying oddities. For one it claims to have a 256 TiB PCI BAR (not
> a typo) which leads to any attempt to mmap() it failing during vmap.
> 
> Even if one tried to map this "BAR" only partially the mapping would not
> be usable on systems with MIO support enabled however. This is because
> of another oddity in that this virtual PCI device does not support the
> newer memory I/O (MIO) PCI instructions and legacy PCI instructions are
> not accessible by user-space when MIO is in use. If this device needs to
> be accessed by user-space it will thus need a vfio-pci variant driver.
> Until then work around both issues by excluding resources which don't
> fit between IOREMAP_START and IOREMAP_END in vfio_pci_probe_mmaps().
> 
> Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
> ---
>  drivers/vfio/pci/vfio_pci_core.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason