Re: [PATCH v2 2/2] vfio: add virtio pci quirk

[Alex Williamson <alex.williamson@redhat.com>]

On Mon, 29 Aug 2016 21:52:20 -0600
Alex Williamson <alex.williamson@redhat.com> wrote:

> On Mon, 29 Aug 2016 21:23:25 -0600
> Alex Williamson <alex.williamson@redhat.com> wrote:
> 
> > On Tue, 30 Aug 2016 05:27:17 +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         |  14 ++++
> > >  drivers/vfio/pci/vfio_pci_virtio.c  | 140 ++++++++++++++++++++++++++++++++++++
> > >  drivers/vfio/pci/Makefile           |   1 +
> > >  4 files changed, 156 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 2128de8..2bd5616 100644
> > > --- a/drivers/vfio/pci/vfio_pci_private.h
> > > +++ b/drivers/vfio/pci/vfio_pci_private.h
> > > @@ -139,4 +139,5 @@ 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, bool noiommu);
> > >  #endif /* VFIO_PCI_PRIVATE_H */
> > > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> > > index d624a52..e93bf0c 100644
> > > --- a/drivers/vfio/pci/vfio_pci.c
> > > +++ b/drivers/vfio/pci/vfio_pci.c
> > > @@ -1236,6 +1236,20 @@ 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) {    
> > 
> > Perhaps a vfio_pci_is_virtio() like vga below?  Let's test the device
> > ID range initially as well, this test raised a big red flag for me
> > whether all devices within this vendor ID were virtio.
> >   
> > > +		bool noiommu = vfio_is_noiommu_group_dev(&pdev->dev);    
> > 
> > I think you can use iommu_present() for this and avoid patch 1of2.
> > noiommu is mutually exclusive to an iommu being present.  Seems like
> > all of this logic should be in the quirk itself, I'm not sure what it
> > buys to get the value here but wait until later to use it.  Using
> > iommu_present() could also move this test much earlier in
> > vfio_pci_probe() making the exit path easier.  
> 
> Except then I'm reintroducing the bug fixed by 16ab8a5cbea4 since
> iommu_present() assumes an IOMMU API based device.  I'll try to think if
> there's another way to avoid adding the is_noiommu function.  Thanks,

I think something like this would do it.

--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -1214,6 +1214,22 @@ static int vfio_pci_probe(struct pci_dev *pdev, const str
        if (pdev->hdr_type != PCI_HEADER_TYPE_NORMAL)
                return -EINVAL;
 
+       /*
+        * Filter out virtio devices that do not honor the iommu,
+        * but only for real iommu groups.
+        */
+       if (vfio_pci_is_virtio(pdev)) {
+               struct iommu_group *tmp = iommu_group_get(&pdev->dev);
+
+               if (tmp) {
+                       iommu_group_put(tmp);
+
+                       ret = vfio_pci_virtio_quirk(pdev);
+                       if (ret)
+                               return ret;
+               }
+       }
+
        group = vfio_iommu_group_get(&pdev->dev);
        if (!group)
                return -EINVAL;

Thanks,
Alex

> > > +
> > > +		ret = vfio_pci_virtio_quirk(vdev, noiommu);
> > > +		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..e1ecffd
> > > --- /dev/null
> > > +++ b/drivers/vfio/pci/vfio_pci_virtio.c
> > > @@ -0,0 +1,140 @@
> > > +/*
> > > + * 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.
> > > + */
> > > +
> > > +#include <linux/io.h>
> > > +#include <linux/pci.h>
> > > +#include <linux/uaccess.h>    
> > 
> > Are io.h and uaccess.h needed?
> >   
> > > +#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)    
> > 
> > Does inlining this really make sense?
> >   
> > > +{
> > > +	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)    
> > 
> > s/0x5/PCI_STD_RESOURCE_END/
> >   
> > > +				continue;
> > > +		}
> > > +
> > > +		return pos;
> > > +	}
> > > +	return 0;
> > > +}
> > > +
> > > +
> > > +int vfio_pci_virtio_quirk(struct vfio_pci_device *vdev, bool noiommu)
> > > +{
> > > +	struct pci_dev *dev = vdev->pdev;    
> > 
> > Please use *pdev for consistency with the rest of drivers/vfio/pci/*
> > 
> > Also, is there any reason to pass the vfio_pci_device?  There's nothing
> > vfio here otherwise and we could remove more #includes.
> >   
> > > +	int common, cfg;
> > > +	u32 features;
> > > +	u32 offset;
> > > +	u8 bar;
> > > +
> > > +	/* Without an IOMMU, we don't care */
> > > +	if (noiommu)
> > > +		return 0;
> > > +
> > > +        /* Virtio only owns devices >= 0x1000 and <= 0x107f: leave the rest. */
> > > +        if (dev->device < 0x1000 || dev->device > 0x107f)
> > > +                return 0;    
> > 
> > Whitespace
> >   
> > > +
> > > +	/* 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");    
> > 
> > Whitespace
> >   
> > > +		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");    
> > 
> > Whitespace
> >   
> > > +		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    
> > 
> > Thanks,
> > Alex