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Date:   Mon, 29 Aug 2016 21:52:20 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Jason Wang <jasowang@...hat.com>,
        Cornelia Huck <cornelia.huck@...ibm.com>,
        virtualization@...ts.linux-foundation.org, qemu-devel@...gnu.org,
        kvm@...r.kernel.org, Julia Lawall <Julia.Lawall@...6.fr>,
        Yongji Xie <xyjxie@...ux.vnet.ibm.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Feng Wu <feng.wu@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v2 2/2] vfio: add virtio pci quirk

On Mon, 29 Aug 2016 21:23:25 -0600
Alex Williamson <alex.williamson@...hat.com> wrote:

> On Tue, 30 Aug 2016 05:27:17 +0300
> "Michael S. Tsirkin" <mst@...hat.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@...hat.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,

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@...hat.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

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