diff mbox

[RFC,3/3] vfio: add virtio pci quirk

Message ID 1460973374-32719-4-git-send-email-mst@redhat.com
State New
Headers show

Commit Message

Michael S. Tsirkin April 18, 2016, 9:58 a.m. UTC
Modern virtio pci devices can set VIRTIO_F_IOMMU_PLATFORM
to signal they are safe to use with an IOMMU.

Without this bit, exposing the device to userspace is unsafe, so probe
and fail VFIO initialization unless noiommu is enabled.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 drivers/vfio/pci/vfio_pci_private.h |   1 +
 drivers/vfio/pci/vfio_pci.c         |  11 +++
 drivers/vfio/pci/vfio_pci_virtio.c  | 135 ++++++++++++++++++++++++++++++++++++
 drivers/vfio/pci/Makefile           |   1 +
 4 files changed, 148 insertions(+)
 create mode 100644 drivers/vfio/pci/vfio_pci_virtio.c

Comments

Alex Williamson April 18, 2016, 8 p.m. UTC | #1
On Mon, 18 Apr 2016 12:58:28 +0300
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> Modern virtio pci devices can set VIRTIO_F_IOMMU_PLATFORM
> to signal they are safe to use with an IOMMU.
> 
> Without this bit, exposing the device to userspace is unsafe, so probe
> and fail VFIO initialization unless noiommu is enabled.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>  drivers/vfio/pci/vfio_pci_private.h |   1 +
>  drivers/vfio/pci/vfio_pci.c         |  11 +++
>  drivers/vfio/pci/vfio_pci_virtio.c  | 135 ++++++++++++++++++++++++++++++++++++
>  drivers/vfio/pci/Makefile           |   1 +
>  4 files changed, 148 insertions(+)
>  create mode 100644 drivers/vfio/pci/vfio_pci_virtio.c
> 
> diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
> index 8a7d546..604d445 100644
> --- a/drivers/vfio/pci/vfio_pci_private.h
> +++ b/drivers/vfio/pci/vfio_pci_private.h
> @@ -130,4 +130,5 @@ static inline int vfio_pci_igd_init(struct vfio_pci_device *vdev)
>  	return -ENODEV;
>  }
>  #endif
> +extern int vfio_pci_virtio_quirk(struct vfio_pci_device *vdev, int noiommu);
>  #endif /* VFIO_PCI_PRIVATE_H */
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index d622a41..2bb8c76 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -1125,6 +1125,17 @@ static int vfio_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  		return ret;
>  	}
>  
> +	if (pdev->vendor == PCI_VENDOR_ID_REDHAT_QUMRANET &&

Virtio really owns this entire vendor ID block?  Apparently nobody told
ivshmem: http://pci-ids.ucw.cz/read/PC/1af4/1110  Even the comment by
virtio_pci_id_table[] suggests virtio is only a subset even if the code
doesn't appear to honor that comment.  I don't know the history there,
but that seems like really inefficient use of an entire, coveted vendor
block.

> +	    ((ret = vfio_pci_virtio_quirk(vdev, ret)))) {

Please don't set variables like this unless necessary.

if (vendor...) {
   ret = vfio_pci_virtio_quir...
   if (ret) {
       ...

> +		dev_warn(&vdev->pdev->dev,
> +			 "Failed to setup Virtio for VFIO\n");
> +		vfio_del_group_dev(&pdev->dev);
> +		vfio_iommu_group_put(group, &pdev->dev);
> +		kfree(vdev);
> +		return ret;
> +	}
> +
> +
>  	if (vfio_pci_is_vga(pdev)) {
>  		vga_client_register(pdev, vdev, NULL, vfio_pci_set_vga_decode);
>  		vga_set_legacy_decoding(pdev,
> diff --git a/drivers/vfio/pci/vfio_pci_virtio.c b/drivers/vfio/pci/vfio_pci_virtio.c
> new file mode 100644
> index 0000000..1a32064
> --- /dev/null
> +++ b/drivers/vfio/pci/vfio_pci_virtio.c
> @@ -0,0 +1,135 @@
> +/*
> + * VFIO PCI Intel Graphics support
> + *
> + * Copyright (C) 2016 Red Hat, Inc.  All rights reserved.
> + *	Author: Alex Williamson <alex.williamson@redhat.com>
> + *

Update

> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * Register a device specific region through which to provide read-only
> + * access to the Intel IGD opregion.  The register defining the opregion
> + * address is also virtualized to prevent user modification.

Update

> + */
> +
> +#include <linux/io.h>
> +#include <linux/pci.h>
> +#include <linux/uaccess.h>
> +#include <linux/vfio.h>
> +#include <linux/virtio_pci.h>
> +#include <linux/virtio_config.h>

I don't see where io or uaccess are needed here.

> +
> +#include "vfio_pci_private.h"
> +
> +/**
> + * virtio_pci_find_capability - walk capabilities to find device info.
> + * @dev: the pci device
> + * @cfg_type: the VIRTIO_PCI_CAP_* value we seek
> + *
> + * Returns offset of the capability, or 0.
> + */
> +static inline int virtio_pci_find_capability(struct pci_dev *dev, u8 cfg_type)

This is called from probe code, why inline?  There's already a function
with this exact same name in virtio code, can we come up with something
unique to avoid confusion?

> +{
> +	int pos;
> +
> +	for (pos = pci_find_capability(dev, PCI_CAP_ID_VNDR);
> +	     pos > 0;
> +	     pos = pci_find_next_capability(dev, pos, PCI_CAP_ID_VNDR)) {
> +		u8 type;
> +		pci_read_config_byte(dev, pos + offsetof(struct virtio_pci_cap,
> +							 cfg_type),
> +				     &type);
> +
> +		if (type != cfg_type)
> +			continue;
> +
> +		/* Ignore structures with reserved BAR values */
> +		if (type != VIRTIO_PCI_CAP_PCI_CFG) {
> +			u8 bar;
> +
> +			pci_read_config_byte(dev, pos +
> +					     offsetof(struct virtio_pci_cap,
> +						      bar),
> +					     &bar);
> +			if (bar > 0x5)
> +				continue;
> +		}
> +
> +		return pos;
> +	}
> +	return 0;
> +}
> +
> +
> +int vfio_pci_virtio_quirk(struct vfio_pci_device *vdev, int noiommu)
> +{
> +	struct pci_dev *dev = vdev->pdev;
> +	int common, cfg;
> +	u32 features;
> +	u32 offset;
> +	u8 bar;
> +
> +	/* Without an IOMMU, we don't care */
> +	if (noiommu)
> +		return 0;
> +	/* Check whether device enforces the IOMMU correctly */
> +
> +	/*
> +	 * All modern devices must have common and cfg capabilities. We use cfg
> +	 * capability for access so that we don't need to worry about resource
> +	 * availability. Slow but sure.
> +	 * Note that all vendor-specific fields we access are little-endian
> +	 * which matches what pci config accessors expect, so they do byteswap
> +	 * for us if appropriate.
> +	 */
> +	common = virtio_pci_find_capability(dev, VIRTIO_PCI_CAP_COMMON_CFG);
> +	cfg = virtio_pci_find_capability(dev, VIRTIO_PCI_CAP_PCI_CFG);
> +	if (!cfg || !common) {
> +                dev_warn(&dev->dev,
> +                         "Virtio device lacks common or pci cfg.\n");

White space

> +		return -ENODEV;
> +	}
> +
> +	pci_read_config_byte(dev, common + offsetof(struct virtio_pci_cap,
> +						    bar),
> +			     &bar);
> +	pci_read_config_dword(dev, common + offsetof(struct virtio_pci_cap,
> +						    offset),
> +			     &offset);
> +
> +	/* Program cfg capability for dword access into common cfg. */
> +	pci_write_config_byte(dev, cfg + offsetof(struct virtio_pci_cfg_cap,
> +						  cap.bar),
> +			      bar);
> +	pci_write_config_dword(dev, cfg + offsetof(struct virtio_pci_cfg_cap,
> +						   cap.length),
> +			       0x4);
> +
> +	/* Select features dword that has VIRTIO_F_IOMMU_PLATFORM. */
> +	pci_write_config_dword(dev, cfg + offsetof(struct virtio_pci_cfg_cap,
> +						  cap.offset),
> +			       offset + offsetof(struct virtio_pci_common_cfg,
> +						 device_feature_select));
> +	pci_write_config_dword(dev, cfg + offsetof(struct virtio_pci_cfg_cap,
> +						  pci_cfg_data),
> +			       VIRTIO_F_IOMMU_PLATFORM / 32);
> +
> +	/* Get the features dword. */
> +	pci_write_config_dword(dev, cfg + offsetof(struct virtio_pci_cfg_cap,
> +						  cap.offset),
> +			       offset + offsetof(struct virtio_pci_common_cfg,
> +						 device_feature));
> +	pci_read_config_dword(dev, cfg + offsetof(struct virtio_pci_cfg_cap,
> +						  pci_cfg_data),
> +			      &features);
> +
> +	/* Does this device obey the platform's IOMMU? If not it's an error. */
> +	if (!(features & (0x1 << (VIRTIO_F_IOMMU_PLATFORM % 32)))) {
> +                dev_warn(&dev->dev,
> +                         "Virtio device lacks VIRTIO_F_IOMMU_PLATFORM.\n");

White space

> +		return -ENODEV;
> +	}
> +
> +	return 0;
> +}
> diff --git a/drivers/vfio/pci/Makefile b/drivers/vfio/pci/Makefile
> index 76d8ec0..e9b20e7 100644
> --- a/drivers/vfio/pci/Makefile
> +++ b/drivers/vfio/pci/Makefile
> @@ -1,5 +1,6 @@
>  
>  vfio-pci-y := vfio_pci.o vfio_pci_intrs.o vfio_pci_rdwr.o vfio_pci_config.o
> +vfio-pci-y += vfio_pci_virtio.o
>  vfio-pci-$(CONFIG_VFIO_PCI_IGD) += vfio_pci_igd.o
>  
>  obj-$(CONFIG_VFIO_PCI) += vfio-pci.o
Michael S. Tsirkin April 19, 2016, 9:58 a.m. UTC | #2
On Mon, Apr 18, 2016 at 02:00:06PM -0600, Alex Williamson wrote:
> On Mon, 18 Apr 2016 12:58:28 +0300
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > Modern virtio pci devices can set VIRTIO_F_IOMMU_PLATFORM
> > to signal they are safe to use with an IOMMU.
> > 
> > Without this bit, exposing the device to userspace is unsafe, so probe
> > and fail VFIO initialization unless noiommu is enabled.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> >  drivers/vfio/pci/vfio_pci_private.h |   1 +
> >  drivers/vfio/pci/vfio_pci.c         |  11 +++
> >  drivers/vfio/pci/vfio_pci_virtio.c  | 135 ++++++++++++++++++++++++++++++++++++
> >  drivers/vfio/pci/Makefile           |   1 +
> >  4 files changed, 148 insertions(+)
> >  create mode 100644 drivers/vfio/pci/vfio_pci_virtio.c
> > 
> > diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
> > index 8a7d546..604d445 100644
> > --- a/drivers/vfio/pci/vfio_pci_private.h
> > +++ b/drivers/vfio/pci/vfio_pci_private.h
> > @@ -130,4 +130,5 @@ static inline int vfio_pci_igd_init(struct vfio_pci_device *vdev)
> >  	return -ENODEV;
> >  }
> >  #endif
> > +extern int vfio_pci_virtio_quirk(struct vfio_pci_device *vdev, int noiommu);
> >  #endif /* VFIO_PCI_PRIVATE_H */
> > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> > index d622a41..2bb8c76 100644
> > --- a/drivers/vfio/pci/vfio_pci.c
> > +++ b/drivers/vfio/pci/vfio_pci.c
> > @@ -1125,6 +1125,17 @@ static int vfio_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> >  		return ret;
> >  	}
> >  
> > +	if (pdev->vendor == PCI_VENDOR_ID_REDHAT_QUMRANET &&
> 
> Virtio really owns this entire vendor ID block?  Apparently nobody told
> ivshmem: http://pci-ids.ucw.cz/read/PC/1af4/1110  Even the comment by
> virtio_pci_id_table[] suggests virtio is only a subset even if the code
> doesn't appear to honor that comment.  I don't know the history there,
> but that seems like really inefficient use of an entire, coveted vendor
> block.

True - virtio spec also says it's up to 0x107f.


> > +	    ((ret = vfio_pci_virtio_quirk(vdev, ret)))) {
> 
> Please don't set variables like this unless necessary.
> 
> if (vendor...) {
>    ret = vfio_pci_virtio_quir...
>    if (ret) {
>        ...
> 
> > +		dev_warn(&vdev->pdev->dev,
> > +			 "Failed to setup Virtio for VFIO\n");
> > +		vfio_del_group_dev(&pdev->dev);
> > +		vfio_iommu_group_put(group, &pdev->dev);
> > +		kfree(vdev);
> > +		return ret;
> > +	}
> > +
> > +
> >  	if (vfio_pci_is_vga(pdev)) {
> >  		vga_client_register(pdev, vdev, NULL, vfio_pci_set_vga_decode);
> >  		vga_set_legacy_decoding(pdev,
> > diff --git a/drivers/vfio/pci/vfio_pci_virtio.c b/drivers/vfio/pci/vfio_pci_virtio.c
> > new file mode 100644
> > index 0000000..1a32064
> > --- /dev/null
> > +++ b/drivers/vfio/pci/vfio_pci_virtio.c
> > @@ -0,0 +1,135 @@
> > +/*
> > + * VFIO PCI Intel Graphics support
> > + *
> > + * Copyright (C) 2016 Red Hat, Inc.  All rights reserved.
> > + *	Author: Alex Williamson <alex.williamson@redhat.com>
> > + *
> 
> Update
> 
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 as
> > + * published by the Free Software Foundation.
> > + *
> > + * Register a device specific region through which to provide read-only
> > + * access to the Intel IGD opregion.  The register defining the opregion
> > + * address is also virtualized to prevent user modification.
> 
> Update
> 
> > + */
> > +
> > +#include <linux/io.h>
> > +#include <linux/pci.h>
> > +#include <linux/uaccess.h>
> > +#include <linux/vfio.h>
> > +#include <linux/virtio_pci.h>
> > +#include <linux/virtio_config.h>
> 
> I don't see where io or uaccess are needed here.
> 
> > +
> > +#include "vfio_pci_private.h"
> > +
> > +/**
> > + * virtio_pci_find_capability - walk capabilities to find device info.
> > + * @dev: the pci device
> > + * @cfg_type: the VIRTIO_PCI_CAP_* value we seek
> > + *
> > + * Returns offset of the capability, or 0.
> > + */
> > +static inline int virtio_pci_find_capability(struct pci_dev *dev, u8 cfg_type)
> 
> This is called from probe code, why inline?  There's already a function
> with this exact same name in virtio code, can we come up with something
> unique to avoid confusion?
> 
> > +{
> > +	int pos;
> > +
> > +	for (pos = pci_find_capability(dev, PCI_CAP_ID_VNDR);
> > +	     pos > 0;
> > +	     pos = pci_find_next_capability(dev, pos, PCI_CAP_ID_VNDR)) {
> > +		u8 type;
> > +		pci_read_config_byte(dev, pos + offsetof(struct virtio_pci_cap,
> > +							 cfg_type),
> > +				     &type);
> > +
> > +		if (type != cfg_type)
> > +			continue;
> > +
> > +		/* Ignore structures with reserved BAR values */
> > +		if (type != VIRTIO_PCI_CAP_PCI_CFG) {
> > +			u8 bar;
> > +
> > +			pci_read_config_byte(dev, pos +
> > +					     offsetof(struct virtio_pci_cap,
> > +						      bar),
> > +					     &bar);
> > +			if (bar > 0x5)
> > +				continue;
> > +		}
> > +
> > +		return pos;
> > +	}
> > +	return 0;
> > +}
> > +
> > +
> > +int vfio_pci_virtio_quirk(struct vfio_pci_device *vdev, int noiommu)
> > +{
> > +	struct pci_dev *dev = vdev->pdev;
> > +	int common, cfg;
> > +	u32 features;
> > +	u32 offset;
> > +	u8 bar;
> > +
> > +	/* Without an IOMMU, we don't care */
> > +	if (noiommu)
> > +		return 0;
> > +	/* Check whether device enforces the IOMMU correctly */
> > +
> > +	/*
> > +	 * All modern devices must have common and cfg capabilities. We use cfg
> > +	 * capability for access so that we don't need to worry about resource
> > +	 * availability. Slow but sure.
> > +	 * Note that all vendor-specific fields we access are little-endian
> > +	 * which matches what pci config accessors expect, so they do byteswap
> > +	 * for us if appropriate.
> > +	 */
> > +	common = virtio_pci_find_capability(dev, VIRTIO_PCI_CAP_COMMON_CFG);
> > +	cfg = virtio_pci_find_capability(dev, VIRTIO_PCI_CAP_PCI_CFG);
> > +	if (!cfg || !common) {
> > +                dev_warn(&dev->dev,
> > +                         "Virtio device lacks common or pci cfg.\n");
> 
> White space
> 
> > +		return -ENODEV;
> > +	}
> > +
> > +	pci_read_config_byte(dev, common + offsetof(struct virtio_pci_cap,
> > +						    bar),
> > +			     &bar);
> > +	pci_read_config_dword(dev, common + offsetof(struct virtio_pci_cap,
> > +						    offset),
> > +			     &offset);
> > +
> > +	/* Program cfg capability for dword access into common cfg. */
> > +	pci_write_config_byte(dev, cfg + offsetof(struct virtio_pci_cfg_cap,
> > +						  cap.bar),
> > +			      bar);
> > +	pci_write_config_dword(dev, cfg + offsetof(struct virtio_pci_cfg_cap,
> > +						   cap.length),
> > +			       0x4);
> > +
> > +	/* Select features dword that has VIRTIO_F_IOMMU_PLATFORM. */
> > +	pci_write_config_dword(dev, cfg + offsetof(struct virtio_pci_cfg_cap,
> > +						  cap.offset),
> > +			       offset + offsetof(struct virtio_pci_common_cfg,
> > +						 device_feature_select));
> > +	pci_write_config_dword(dev, cfg + offsetof(struct virtio_pci_cfg_cap,
> > +						  pci_cfg_data),
> > +			       VIRTIO_F_IOMMU_PLATFORM / 32);
> > +
> > +	/* Get the features dword. */
> > +	pci_write_config_dword(dev, cfg + offsetof(struct virtio_pci_cfg_cap,
> > +						  cap.offset),
> > +			       offset + offsetof(struct virtio_pci_common_cfg,
> > +						 device_feature));
> > +	pci_read_config_dword(dev, cfg + offsetof(struct virtio_pci_cfg_cap,
> > +						  pci_cfg_data),
> > +			      &features);
> > +
> > +	/* Does this device obey the platform's IOMMU? If not it's an error. */
> > +	if (!(features & (0x1 << (VIRTIO_F_IOMMU_PLATFORM % 32)))) {
> > +                dev_warn(&dev->dev,
> > +                         "Virtio device lacks VIRTIO_F_IOMMU_PLATFORM.\n");
> 
> White space
> 
> > +		return -ENODEV;
> > +	}
> > +
> > +	return 0;
> > +}
> > diff --git a/drivers/vfio/pci/Makefile b/drivers/vfio/pci/Makefile
> > index 76d8ec0..e9b20e7 100644
> > --- a/drivers/vfio/pci/Makefile
> > +++ b/drivers/vfio/pci/Makefile
> > @@ -1,5 +1,6 @@
> >  
> >  vfio-pci-y := vfio_pci.o vfio_pci_intrs.o vfio_pci_rdwr.o vfio_pci_config.o
> > +vfio-pci-y += vfio_pci_virtio.o
> >  vfio-pci-$(CONFIG_VFIO_PCI_IGD) += vfio_pci_igd.o
> >  
> >  obj-$(CONFIG_VFIO_PCI) += vfio-pci.o
diff mbox

Patch

diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
index 8a7d546..604d445 100644
--- a/drivers/vfio/pci/vfio_pci_private.h
+++ b/drivers/vfio/pci/vfio_pci_private.h
@@ -130,4 +130,5 @@  static inline int vfio_pci_igd_init(struct vfio_pci_device *vdev)
 	return -ENODEV;
 }
 #endif
+extern int vfio_pci_virtio_quirk(struct vfio_pci_device *vdev, int noiommu);
 #endif /* VFIO_PCI_PRIVATE_H */
diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index d622a41..2bb8c76 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -1125,6 +1125,17 @@  static int vfio_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 		return ret;
 	}
 
+	if (pdev->vendor == PCI_VENDOR_ID_REDHAT_QUMRANET &&
+	    ((ret = vfio_pci_virtio_quirk(vdev, ret)))) {
+		dev_warn(&vdev->pdev->dev,
+			 "Failed to setup Virtio for VFIO\n");
+		vfio_del_group_dev(&pdev->dev);
+		vfio_iommu_group_put(group, &pdev->dev);
+		kfree(vdev);
+		return ret;
+	}
+
+
 	if (vfio_pci_is_vga(pdev)) {
 		vga_client_register(pdev, vdev, NULL, vfio_pci_set_vga_decode);
 		vga_set_legacy_decoding(pdev,
diff --git a/drivers/vfio/pci/vfio_pci_virtio.c b/drivers/vfio/pci/vfio_pci_virtio.c
new file mode 100644
index 0000000..1a32064
--- /dev/null
+++ b/drivers/vfio/pci/vfio_pci_virtio.c
@@ -0,0 +1,135 @@ 
+/*
+ * VFIO PCI Intel Graphics support
+ *
+ * Copyright (C) 2016 Red Hat, Inc.  All rights reserved.
+ *	Author: Alex Williamson <alex.williamson@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * Register a device specific region through which to provide read-only
+ * access to the Intel IGD opregion.  The register defining the opregion
+ * address is also virtualized to prevent user modification.
+ */
+
+#include <linux/io.h>
+#include <linux/pci.h>
+#include <linux/uaccess.h>
+#include <linux/vfio.h>
+#include <linux/virtio_pci.h>
+#include <linux/virtio_config.h>
+
+#include "vfio_pci_private.h"
+
+/**
+ * virtio_pci_find_capability - walk capabilities to find device info.
+ * @dev: the pci device
+ * @cfg_type: the VIRTIO_PCI_CAP_* value we seek
+ *
+ * Returns offset of the capability, or 0.
+ */
+static inline int virtio_pci_find_capability(struct pci_dev *dev, u8 cfg_type)
+{
+	int pos;
+
+	for (pos = pci_find_capability(dev, PCI_CAP_ID_VNDR);
+	     pos > 0;
+	     pos = pci_find_next_capability(dev, pos, PCI_CAP_ID_VNDR)) {
+		u8 type;
+		pci_read_config_byte(dev, pos + offsetof(struct virtio_pci_cap,
+							 cfg_type),
+				     &type);
+
+		if (type != cfg_type)
+			continue;
+
+		/* Ignore structures with reserved BAR values */
+		if (type != VIRTIO_PCI_CAP_PCI_CFG) {
+			u8 bar;
+
+			pci_read_config_byte(dev, pos +
+					     offsetof(struct virtio_pci_cap,
+						      bar),
+					     &bar);
+			if (bar > 0x5)
+				continue;
+		}
+
+		return pos;
+	}
+	return 0;
+}
+
+
+int vfio_pci_virtio_quirk(struct vfio_pci_device *vdev, int noiommu)
+{
+	struct pci_dev *dev = vdev->pdev;
+	int common, cfg;
+	u32 features;
+	u32 offset;
+	u8 bar;
+
+	/* Without an IOMMU, we don't care */
+	if (noiommu)
+		return 0;
+	/* Check whether device enforces the IOMMU correctly */
+
+	/*
+	 * All modern devices must have common and cfg capabilities. We use cfg
+	 * capability for access so that we don't need to worry about resource
+	 * availability. Slow but sure.
+	 * Note that all vendor-specific fields we access are little-endian
+	 * which matches what pci config accessors expect, so they do byteswap
+	 * for us if appropriate.
+	 */
+	common = virtio_pci_find_capability(dev, VIRTIO_PCI_CAP_COMMON_CFG);
+	cfg = virtio_pci_find_capability(dev, VIRTIO_PCI_CAP_PCI_CFG);
+	if (!cfg || !common) {
+                dev_warn(&dev->dev,
+                         "Virtio device lacks common or pci cfg.\n");
+		return -ENODEV;
+	}
+
+	pci_read_config_byte(dev, common + offsetof(struct virtio_pci_cap,
+						    bar),
+			     &bar);
+	pci_read_config_dword(dev, common + offsetof(struct virtio_pci_cap,
+						    offset),
+			     &offset);
+
+	/* Program cfg capability for dword access into common cfg. */
+	pci_write_config_byte(dev, cfg + offsetof(struct virtio_pci_cfg_cap,
+						  cap.bar),
+			      bar);
+	pci_write_config_dword(dev, cfg + offsetof(struct virtio_pci_cfg_cap,
+						   cap.length),
+			       0x4);
+
+	/* Select features dword that has VIRTIO_F_IOMMU_PLATFORM. */
+	pci_write_config_dword(dev, cfg + offsetof(struct virtio_pci_cfg_cap,
+						  cap.offset),
+			       offset + offsetof(struct virtio_pci_common_cfg,
+						 device_feature_select));
+	pci_write_config_dword(dev, cfg + offsetof(struct virtio_pci_cfg_cap,
+						  pci_cfg_data),
+			       VIRTIO_F_IOMMU_PLATFORM / 32);
+
+	/* Get the features dword. */
+	pci_write_config_dword(dev, cfg + offsetof(struct virtio_pci_cfg_cap,
+						  cap.offset),
+			       offset + offsetof(struct virtio_pci_common_cfg,
+						 device_feature));
+	pci_read_config_dword(dev, cfg + offsetof(struct virtio_pci_cfg_cap,
+						  pci_cfg_data),
+			      &features);
+
+	/* Does this device obey the platform's IOMMU? If not it's an error. */
+	if (!(features & (0x1 << (VIRTIO_F_IOMMU_PLATFORM % 32)))) {
+                dev_warn(&dev->dev,
+                         "Virtio device lacks VIRTIO_F_IOMMU_PLATFORM.\n");
+		return -ENODEV;
+	}
+
+	return 0;
+}
diff --git a/drivers/vfio/pci/Makefile b/drivers/vfio/pci/Makefile
index 76d8ec0..e9b20e7 100644
--- a/drivers/vfio/pci/Makefile
+++ b/drivers/vfio/pci/Makefile
@@ -1,5 +1,6 @@ 
 
 vfio-pci-y := vfio_pci.o vfio_pci_intrs.o vfio_pci_rdwr.o vfio_pci_config.o
+vfio-pci-y += vfio_pci_virtio.o
 vfio-pci-$(CONFIG_VFIO_PCI_IGD) += vfio_pci_igd.o
 
 obj-$(CONFIG_VFIO_PCI) += vfio-pci.o