From: Yishai Hadas <yishaih@nvidia.com>
Date: Tue, 17 Mar 2026 16:17:49 +0000 (+0200)
Subject: vfio: Add support for VFIO_DEVICE_FEATURE_MIG_PRECOPY_INFOv2
X-Git-Tag: v7.1-rc1~132^2~15
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=50ff3f404617c5d15832fec3711978104c4c9efd;p=thirdparty%2Fkernel%2Fstable.git

vfio: Add support for VFIO_DEVICE_FEATURE_MIG_PRECOPY_INFOv2

Currently, existing VFIO_MIG_GET_PRECOPY_INFO implementations don't
assign info.flags before copy_to_user().

Because they copy the struct in from userspace first, this effectively
echoes userspace-provided flags back as output, preventing the field
from being used to report new reliable data from the drivers.

Add support for a new device feature named
VFIO_DEVICE_FEATURE_MIG_PRECOPY_INFOv2.

On SET, enables the v2 pre_copy_info behaviour, where the
vfio_precopy_info.flags is a valid output field.

Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Link: https://lore.kernel.org/r/20260317161753.18964-3-yishaih@nvidia.com
Signed-off-by: Alex Williamson <alex@shazbot.org>
---

diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
index 742477546b15d..8666f35fb3f0d 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -553,6 +553,7 @@ static void vfio_df_device_last_close(struct vfio_device_file *df)
 		vfio_df_iommufd_unbind(df);
 	else
 		vfio_device_group_unuse_iommu(device);
+	device->precopy_info_v2 = 0;
 	module_put(device->dev->driver->owner);
 }
 
@@ -964,6 +965,23 @@ vfio_ioctl_device_feature_migration_data_size(struct vfio_device *device,
 	return 0;
 }
 
+static int
+vfio_ioctl_device_feature_migration_precopy_info_v2(struct vfio_device *device,
+						    u32 flags, size_t argsz)
+{
+	int ret;
+
+	if (!(device->migration_flags & VFIO_MIGRATION_PRE_COPY))
+		return -EINVAL;
+
+	ret = vfio_check_feature(flags, argsz, VFIO_DEVICE_FEATURE_SET, 0);
+	if (ret != 1)
+		return ret;
+
+	device->precopy_info_v2 = 1;
+	return 0;
+}
+
 static int vfio_ioctl_device_feature_migration(struct vfio_device *device,
 					       u32 flags, void __user *arg,
 					       size_t argsz)
@@ -1251,6 +1269,9 @@ static int vfio_ioctl_device_feature(struct vfio_device *device,
 		return vfio_ioctl_device_feature_migration_data_size(
 			device, feature.flags, arg->data,
 			feature.argsz - minsz);
+	case VFIO_DEVICE_FEATURE_MIG_PRECOPY_INFOv2:
+		return vfio_ioctl_device_feature_migration_precopy_info_v2(
+			device, feature.flags, feature.argsz - minsz);
 	default:
 		if (unlikely(!device->ops->device_feature))
 			return -ENOTTY;
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index e90859956514a..7c1d33283e042 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -52,6 +52,7 @@ struct vfio_device {
 	struct vfio_device_set *dev_set;
 	struct list_head dev_set_list;
 	unsigned int migration_flags;
+	u8 precopy_info_v2;
 	struct kvm *kvm;
 
 	/* Members below here are private, not for driver use */