Re: [PATCH v0 06/15] mshv: Implement mshv bridge device for VFIO

Stanislav Kinsburskii
2026-01-20T16:09:02Z

On Mon, Jan 19, 2026 at 10:42:21PM -0800, Mukesh R wrote:
> From: Mukesh Rathor <mrathor@linux.microsoft.com>
>
> Add a new file to implement VFIO-MSHV bridge pseudo device. These
> functions are called in the VFIO framework, and credits to kvm/vfio.c
> as this file was adapted from it.
>
> Original author: Wei Liu <wei.liu@kernel.org>
> (Slightly modified from the original version).
>

There is a Linux standard for giving credits when code is adapted from.
This doesn't follow that standard. Please fix.

> Signed-off-by: Mukesh Rathor <mrathor@linux.microsoft.com>
> ---
> drivers/hv/Makefile | 3 +-
> drivers/hv/mshv_vfio.c | 210 +++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 212 insertions(+), 1 deletion(-)
> create mode 100644 drivers/hv/mshv_vfio.c
>
> diff --git a/drivers/hv/Makefile b/drivers/hv/Makefile
> index a49f93c2d245..eae003c4cb8f 100644
> --- a/drivers/hv/Makefile
> +++ b/drivers/hv/Makefile
> @@ -14,7 +14,8 @@ hv_vmbus-y := vmbus_drv.o \
> hv_vmbus-$(CONFIG_HYPERV_TESTING) += hv_debugfs.o
> hv_utils-y := hv_util.o hv_kvp.o hv_snapshot.o hv_utils_transport.o
> mshv_root-y := mshv_root_main.o mshv_synic.o mshv_eventfd.o mshv_irq.o \
> - mshv_root_hv_call.o mshv_portid_table.o mshv_regions.o
> + mshv_root_hv_call.o mshv_portid_table.o mshv_regions.o \
> + mshv_vfio.o
> mshv_vtl-y := mshv_vtl_main.o
>
> # Code that must be built-in
> diff --git a/drivers/hv/mshv_vfio.c b/drivers/hv/mshv_vfio.c
> new file mode 100644
> index 000000000000..6ea4d99a3bd2
> --- /dev/null
> +++ b/drivers/hv/mshv_vfio.c
> @@ -0,0 +1,210 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * VFIO-MSHV bridge pseudo device
> + *
> + * Heavily inspired by the VFIO-KVM bridge pseudo device.
> + */
> +#include <linux/errno.h>
> +#include <linux/file.h>
> +#include <linux/list.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/slab.h>
> +#include <linux/vfio.h>
> +
> +#include "mshv.h"
> +#include "mshv_root.h"
> +
> +struct mshv_vfio_file {
> + struct list_head node;
> + struct file *file; /* list of struct mshv_vfio_file */
> +};
> +
> +struct mshv_vfio {
> + struct list_head file_list;
> + struct mutex lock;
> +};
> +
> +static bool mshv_vfio_file_is_valid(struct file *file)
> +{
> + bool (*fn)(struct file *file);
> + bool ret;
> +
> + fn = symbol_get(vfio_file_is_valid);
> + if (!fn)
> + return false;
> +
> + ret = fn(file);
> +
> + symbol_put(vfio_file_is_valid);
> +
> + return ret;
> +}
> +
> +static long mshv_vfio_file_add(struct mshv_device *mshvdev, unsigned int fd)
> +{
> + struct mshv_vfio *mshv_vfio = mshvdev->device_private;
> + struct mshv_vfio_file *mvf;
> + struct file *filp;
> + long ret = 0;
> +
> + filp = fget(fd);
> + if (!filp)
> + return -EBADF;
> +
> + /* Ensure the FD is a vfio FD. */
> + if (!mshv_vfio_file_is_valid(filp)) {
> + ret = -EINVAL;
> + goto out_fput;
> + }
> +
> + mutex_lock(&mshv_vfio->lock);
> +
> + list_for_each_entry(mvf, &mshv_vfio->file_list, node) {
> + if (mvf->file == filp) {
> + ret = -EEXIST;
> + goto out_unlock;
> + }
> + }
> +
> + mvf = kzalloc(sizeof(*mvf), GFP_KERNEL_ACCOUNT);
> + if (!mvf) {
> + ret = -ENOMEM;
> + goto out_unlock;
> + }
> +
> + mvf->file = get_file(filp);
> + list_add_tail(&mvf->node, &mshv_vfio->file_list);
> +
> +out_unlock:
> + mutex_unlock(&mshv_vfio->lock);
> +out_fput:
> + fput(filp);
> + return ret;
> +}
> +
> +static long mshv_vfio_file_del(struct mshv_device *mshvdev, unsigned int fd)
> +{
> + struct mshv_vfio *mshv_vfio = mshvdev->device_private;
> + struct mshv_vfio_file *mvf;
> + long ret;
> +
> + CLASS(fd, f)(fd);
> +
> + if (fd_empty(f))
> + return -EBADF;
> +
> + ret = -ENOENT;
> + mutex_lock(&mshv_vfio->lock);
> +
> + list_for_each_entry(mvf, &mshv_vfio->file_list, node) {
> + if (mvf->file != fd_file(f))
> + continue;
> +
> + list_del(&mvf->node);
> + fput(mvf->file);
> + kfree(mvf);
> + ret = 0;
> + break;
> + }
> +
> + mutex_unlock(&mshv_vfio->lock);
> + return ret;
> +}
> +
> +static long mshv_vfio_set_file(struct mshv_device *mshvdev, long attr,
> + void __user *arg)
> +{
> + int32_t __user *argp = arg;
> + int32_t fd;
> +
> + switch (attr) {
> + case MSHV_DEV_VFIO_FILE_ADD:
> + if (get_user(fd, argp))
> + return -EFAULT;
> + return mshv_vfio_file_add(mshvdev, fd);
> +
> + case MSHV_DEV_VFIO_FILE_DEL:
> + if (get_user(fd, argp))
> + return -EFAULT;
> + return mshv_vfio_file_del(mshvdev, fd);
> + }
> +
> + return -ENXIO;
> +}
> +
> +static long mshv_vfio_set_attr(struct mshv_device *mshvdev,
> + struct mshv_device_attr *attr)
> +{
> + switch (attr->group) {
> + case MSHV_DEV_VFIO_FILE:
> + return mshv_vfio_set_file(mshvdev, attr->attr,
> + u64_to_user_ptr(attr->addr));
> + }
> +
> + return -ENXIO;
> +}
> +
> +static long mshv_vfio_has_attr(struct mshv_device *mshvdev,
> + struct mshv_device_attr *attr)
> +{
> + switch (attr->group) {
> + case MSHV_DEV_VFIO_FILE:
> + switch (attr->attr) {
> + case MSHV_DEV_VFIO_FILE_ADD:
> + case MSHV_DEV_VFIO_FILE_DEL:
> + return 0;
> + }
> +
> + break;
> + }
> +
> + return -ENXIO;
> +}
> +
> +static long mshv_vfio_create_device(struct mshv_device *mshvdev, u32 type)
> +{
> + struct mshv_device *tmp;
> + struct mshv_vfio *mshv_vfio;
> +
> + /* Only one VFIO "device" per VM */
> + hlist_for_each_entry(tmp, &mshvdev->device_pt->pt_devices,
> + device_ptnode)
> + if (tmp->device_ops == &mshv_vfio_device_ops)
> + return -EBUSY;
> +
> + mshv_vfio = kzalloc(sizeof(*mshv_vfio), GFP_KERNEL_ACCOUNT);
> + if (mshv_vfio == NULL)
> + return -ENOMEM;
> +
> + INIT_LIST_HEAD(&mshv_vfio->file_list);
> + mutex_init(&mshv_vfio->lock);
> +
> + mshvdev->device_private = mshv_vfio;
> +
> + return 0;
> +}
> +
> +/* This is called from mshv_device_fop_release() */
> +static void mshv_vfio_release_device(struct mshv_device *mshvdev)
> +{
> + struct mshv_vfio *mv = mshvdev->device_private;
> + struct mshv_vfio_file *mvf, *tmp;
> +
> + list_for_each_entry_safe(mvf, tmp, &mv->file_list, node) {
> + fput(mvf->file);

This put must be sync as device must be detached from domain before
attempting partition destruction.
This was explicitly mentioned in the patch originated this code.
Please fix, add a comment and credits to the commit message.

Thanks,
Stanislav

> + list_del(&mvf->node);
> + kfree(mvf);
> + }
> +
> + kfree(mv);
> + kfree(mshvdev);
> +}
> +
> +struct mshv_device_ops mshv_vfio_device_ops = {
> + .device_name = "mshv-vfio",
> + .device_create = mshv_vfio_create_device,
> + .device_release = mshv_vfio_release_device,
> + .device_set_attr = mshv_vfio_set_attr,
> + .device_has_attr = mshv_vfio_has_attr,
> +};
> --
> 2.51.2.vfs.0.1
>