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

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Date: Tue, 18 Jun 2024 09:51:34 -0600
From: Alex Williamson <alex.williamson@...hat.com>
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>, 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 Wed, 29 May 2024 13:36:25 +0200
Niklas Schnelle <schnelle@...ux.ibm.com> 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>
> Reviewed-by: Matthew Rosato <mjrosato@...ux.ibm.com>
> Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
> ---
>  drivers/vfio/pci/vfio_pci_core.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index 80cae87fff36..0f1ddf2d3ef2 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -28,6 +28,7 @@
>  #include <linux/nospec.h>
>  #include <linux/sched/mm.h>
>  #include <linux/iommufd.h>
> +#include <linux/ioremap.h>
>  #if IS_ENABLED(CONFIG_EEH)
>  #include <asm/eeh.h>
>  #endif
> @@ -129,9 +130,12 @@ static void vfio_pci_probe_mmaps(struct vfio_pci_core_device *vdev)
>  		/*
>  		 * The PCI core shouldn't set up a resource with a
>  		 * type but zero size. But there may be bugs that
> -		 * cause us to do that.
> +		 * cause us to do that. There is also at least one
> +		 * device which advertises a resource too large to
> +		 * ioremap().
>  		 */
> -		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,

Alex