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

Alex Williamson
2016-04-18T20:00:06Z

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