linux-kernel - Re: [PATCH v2 2/3] vfio/pci: Tolerate oversized BARs by disallowing mmap

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Message-ID: <67fb5c3d-a53f-4ef3-93de-a307777ec044@linux.ibm.com>
Date: Tue, 28 May 2024 11:13:35 -0400
From: Matthew Rosato <mjrosato@...ux.ibm.com>
To: 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>,
        Alex Williamson <alex.williamson@...hat.com>,
        Gerd Bayer <gbayer@...ux.ibm.com>, Jason Gunthorpe <jgg@...pe.ca>
Cc: linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH v2 2/3] vfio/pci: Tolerate oversized BARs by disallowing
 mmap

On 5/23/24 7:10 AM, 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().
> 
> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
> Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
> ---


Reviewed-by: Matthew Rosato <mjrosato@...ux.ibm.com>