Re: [Qemu-devel] [PATCH RFC 3/3] vfio: add virtio pci quirk

["Michael S. Tsirkin" <mst@redhat.com>]

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