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

Alex Williamson
2016-08-30T03:23:25Z

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.

> +
> + 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