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>
---
 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,
+};
-- 
2.51.2.vfs.0.1

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>

> ---
>  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,
> +};

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,
>> +};
>

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
>