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

Mukesh R
2026-01-24T00:37:36Z

On 1/23/26 10:32, Nuno Das Neves wrote:
> On 1/19/2026 10:42 PM, 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).
>>
>> Signed-off-by: Mukesh Rathor <mrathor@linux.microsoft.com>
>
> Since the code is very similar to Wei's original commit, the way I'd
> recommend to do it is:
> 1. Change the commit author to Wei, using git commit --amend --author=
> and
> 2. Put his signed-off line before yours:
>
> Signed-off-by: Wei Liu <wei.liu@kernel.org>
> Signed-off-by: Mukesh Rathor <mrathor@linux.microsoft.com>
>
> This shows he is the author of the commit but you ported it.
>
> If you feel you changed it enough that it should be considered
> co-authored, you can instead keep your authorship of the commit and
> put:
>
> Co-developed-by: Wei Liu <wei.liu@kernel.org>
> Signed-off-by: Wei Liu <wei.liu@kernel.org>
> Signed-off-by: Mukesh Rathor <mrathor@linux.microsoft.com>

Perfect! Thank you, that is exactly the information I was trying to
seek... makes sense.

Thanks,
-Mukesh

>> ---
>> 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);
>> + 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,
>> +};
>