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

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

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 &&
+	    ((ret = vfio_pci_virtio_quirk(vdev, 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>
+ *
+ * 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>
+#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)
+{
+	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");
+		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");
+		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
-- 
MST