[PATCH v4 0/3] vhost/vsock: fix device IOTLB feature lifecycle

[PATCH v4 0/3] vhost/vsock: fix device IOTLB feature lifecycle

[Jia Jia]

vhost-vsock leaves the device IOTLB attached when userspace clears
VIRTIO_F_ACCESS_PLATFORM. It also replaces an existing IOTLB with an
empty one whenever a later feature update keeps ACCESS_PLATFORM enabled.

Patch 1 adds a common vhost helper that detaches the device IOTLB from
all virtqueues, clears their metadata caches, drops queued IOTLB miss
messages, and frees the old table after all virtqueues have released
their pointers.

Patch 2 uses the helper when vhost-vsock clears ACCESS_PLATFORM. The
acked_features update remains in the vhost-vsock-specific loop.

Patch 3 avoids replacing an existing IOTLB when ACCESS_PLATFORM remains
enabled across a feature update.

Changes since v3:
- move the IOTLB teardown helper from vhost-vsock into common vhost code
- keep acked_features updates in the backend-specific loop
- add the common helper as a separate first patch

Jia Jia (3):
  vhost: add helper to clear device IOTLB
  vhost/vsock: discard IOTLB when ACCESS_PLATFORM is cleared
  vhost/vsock: keep IOTLB across feature updates

 drivers/vhost/vhost.c | 24 ++++++++++++++++++++++++
 drivers/vhost/vhost.h |  1 +
 drivers/vhost/vsock.c |  7 ++++++-
 3 files changed, 31 insertions(+), 1 deletion(-)

-- 
2.34.1

[PATCH v4 1/3] vhost: add helper to clear device IOTLB

[Jia Jia]

The device IOTLB is shared by vhost backends, but clearing it requires
dropping each virtqueue's IOTLB pointer and metadata cache before the
old table is freed. Add a common helper for this teardown sequence so
backend-specific feature code only needs to decide when the table must
be cleared.

The caller must hold the device mutex. The helper does not update
acked_features; backends continue to update that state in their own
virtqueue loops.

Signed-off-by: Jia Jia <physicalmtea@gmail.com>
---
 drivers/vhost/vhost.c | 24 ++++++++++++++++++++++++
 drivers/vhost/vhost.h |  1 +
 2 files changed, 25 insertions(+)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 269efad90369..7eaa61d9ceeb 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2283,6 +2283,30 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
 }
 EXPORT_SYMBOL_GPL(vhost_vring_ioctl);
 
+/* Caller must hold the device mutex. */
+void vhost_clear_device_iotlb(struct vhost_dev *d)
+{
+	struct vhost_iotlb *iotlb;
+	int i;
+
+	iotlb = d->iotlb;
+	d->iotlb = NULL;
+
+	for (i = 0; i < d->nvqs; ++i) {
+		struct vhost_virtqueue *vq = d->vqs[i];
+
+		mutex_lock(&vq->mutex);
+		vq->iotlb = NULL;
+		__vhost_vq_meta_reset(vq);
+		mutex_unlock(&vq->mutex);
+	}
+
+	vhost_clear_msg(d);
+	vhost_iotlb_free(iotlb);
+	wake_up_interruptible_poll(&d->wait, EPOLLIN | EPOLLRDNORM);
+}
+EXPORT_SYMBOL_GPL(vhost_clear_device_iotlb);
+
 int vhost_init_device_iotlb(struct vhost_dev *d)
 {
 	struct vhost_iotlb *niotlb, *oiotlb;
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 0192ade6e749..3c75e8089373 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -277,6 +277,7 @@ ssize_t vhost_chr_read_iter(struct vhost_dev *dev, struct iov_iter *to,
 			    int noblock);
 ssize_t vhost_chr_write_iter(struct vhost_dev *dev,
 			     struct iov_iter *from);
+void vhost_clear_device_iotlb(struct vhost_dev *d);
 int vhost_init_device_iotlb(struct vhost_dev *d);
 
 void vhost_iotlb_map_free(struct vhost_iotlb *iotlb,
-- 
2.34.1

Re: [PATCH v4 1/3] vhost: add helper to clear device IOTLB

[Stefano Garzarella]

On Fri, Aug 14, 2026 at 03:29:01PM +0800, Jia Jia wrote:
>The device IOTLB is shared by vhost backends, but clearing it requires
>dropping each virtqueue's IOTLB pointer and metadata cache before the
>old table is freed. Add a common helper for this teardown sequence so
>backend-specific feature code only needs to decide when the table must
>be cleared.
>
>The caller must hold the device mutex. The helper does not update
>acked_features; backends continue to update that state in their own
>virtqueue loops.
>
>Signed-off-by: Jia Jia <physicalmtea@gmail.com>
>---
> drivers/vhost/vhost.c | 24 ++++++++++++++++++++++++
> drivers/vhost/vhost.h |  1 +
> 2 files changed, 25 insertions(+)
>
>diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>index 269efad90369..7eaa61d9ceeb 100644
>--- a/drivers/vhost/vhost.c
>+++ b/drivers/vhost/vhost.c
>@@ -2283,6 +2283,30 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
> }
> EXPORT_SYMBOL_GPL(vhost_vring_ioctl);
>
>+/* Caller must hold the device mutex. */
>+void vhost_clear_device_iotlb(struct vhost_dev *d)
>+{
>+	struct vhost_iotlb *iotlb;
>+	int i;

Should we move the check of `d->iotlb` here? so the callers doesn't need 
to access to an internal details.

Stefano

>+
>+	iotlb = d->iotlb;
>+	d->iotlb = NULL;
>+
>+	for (i = 0; i < d->nvqs; ++i) {
>+		struct vhost_virtqueue *vq = d->vqs[i];
>+
>+		mutex_lock(&vq->mutex);
>+		vq->iotlb = NULL;
>+		__vhost_vq_meta_reset(vq);
>+		mutex_unlock(&vq->mutex);
>+	}
>+
>+	vhost_clear_msg(d);
>+	vhost_iotlb_free(iotlb);
>+	wake_up_interruptible_poll(&d->wait, EPOLLIN | EPOLLRDNORM);
>+}
>+EXPORT_SYMBOL_GPL(vhost_clear_device_iotlb);
>+
> int vhost_init_device_iotlb(struct vhost_dev *d)
> {
> 	struct vhost_iotlb *niotlb, *oiotlb;
>diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
>index 0192ade6e749..3c75e8089373 100644
>--- a/drivers/vhost/vhost.h
>+++ b/drivers/vhost/vhost.h
>@@ -277,6 +277,7 @@ ssize_t vhost_chr_read_iter(struct vhost_dev *dev, struct iov_iter *to,
> 			    int noblock);
> ssize_t vhost_chr_write_iter(struct vhost_dev *dev,
> 			     struct iov_iter *from);
>+void vhost_clear_device_iotlb(struct vhost_dev *d);
> int vhost_init_device_iotlb(struct vhost_dev *d);
>
> void vhost_iotlb_map_free(struct vhost_iotlb *iotlb,
>-- 
>2.34.1
>

[PATCH v4 2/3] vhost/vsock: discard IOTLB when ACCESS_PLATFORM is cleared

[Jia Jia]

vhost_vsock_set_features() leaves the device IOTLB attached when
userspace clears VIRTIO_F_ACCESS_PLATFORM. Descriptors can therefore
continue to use translations installed before the feature change,
including HVAs made stale by a later memory table update.

Use the common vhost helper to detach the device IOTLB before
acknowledging a feature mask without ACCESS_PLATFORM. The helper clears
each virtqueue's IOTLB pointer and metadata cache under its mutex, then
frees the old IOTLB after all virtqueues have dropped their references.

Fixes: e13a6915a03f ("vhost/vsock: add IOTLB API support")
Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jia Jia <physicalmtea@gmail.com>
---
 drivers/vhost/vsock.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 9aaab6bb8061..b69c260eaeff 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -863,7 +863,11 @@ static int vhost_vsock_set_features(struct vhost_vsock *vsock, u64 features)
 	if ((features & (1 << VHOST_F_LOG_ALL)) &&
 	    !vhost_log_access_ok(&vsock->dev)) {
 		goto err;
 	}
 
+	if (!(features & (1ULL << VIRTIO_F_ACCESS_PLATFORM)) &&
+	    vsock->dev.iotlb)
+		vhost_clear_device_iotlb(&vsock->dev);
+
 	if ((features & (1ULL << VIRTIO_F_ACCESS_PLATFORM))) {
 		if (vhost_init_device_iotlb(&vsock->dev))
 			goto err;
-- 
2.34.1

Re: [PATCH v4 2/3] vhost/vsock: discard IOTLB when ACCESS_PLATFORM is cleared

[Stefano Garzarella]

On Fri, Aug 14, 2026 at 03:29:02PM +0800, Jia Jia wrote:
>vhost_vsock_set_features() leaves the device IOTLB attached when
>userspace clears VIRTIO_F_ACCESS_PLATFORM. Descriptors can therefore
>continue to use translations installed before the feature change,
>including HVAs made stale by a later memory table update.
>
>Use the common vhost helper to detach the device IOTLB before
>acknowledging a feature mask without ACCESS_PLATFORM. The helper clears
>each virtqueue's IOTLB pointer and metadata cache under its mutex, then
>frees the old IOTLB after all virtqueues have dropped their references.
>
>Fixes: e13a6915a03f ("vhost/vsock: add IOTLB API support")
>Suggested-by: Michael S. Tsirkin <mst@redhat.com>
>Signed-off-by: Jia Jia <physicalmtea@gmail.com>
>---
> drivers/vhost/vsock.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
>diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>index 9aaab6bb8061..b69c260eaeff 100644
>--- a/drivers/vhost/vsock.c
>+++ b/drivers/vhost/vsock.c
>@@ -863,7 +863,11 @@ static int vhost_vsock_set_features(struct vhost_vsock *vsock, u64 features)
> 	if ((features & (1 << VHOST_F_LOG_ALL)) &&
> 	    !vhost_log_access_ok(&vsock->dev)) {
> 		goto err;
> 	}
>
>+	if (!(features & (1ULL << VIRTIO_F_ACCESS_PLATFORM)) &&
>+	    vsock->dev.iotlb)
>+		vhost_clear_device_iotlb(&vsock->dev);
>+

Why checking the feature again instead of adding an `else if` in the 
already existing check?

I mean this...

> 	if ((features & (1ULL << VIRTIO_F_ACCESS_PLATFORM))) {
> 		if (vhost_init_device_iotlb(&vsock->dev))
> 			goto err;
	} else if (vsock->dev.iotlb) {
		vhost_clear_device_iotlb(&vsock->dev);
	}

>-- 2.34.1
>

[PATCH v4 3/3] vhost/vsock: keep IOTLB across feature updates

[Jia Jia]

VHOST_SET_FEATURES is also used to update logging while a device is
running. When ACCESS_PLATFORM stays enabled, allocating a new empty
IOTLB on every call drops valid translations and forces avoidable
misses.

Initialize the device IOTLB only when one does not already exist.

Fixes: e13a6915a03f ("vhost/vsock: add IOTLB API support")
Signed-off-by: Jia Jia <physicalmtea@gmail.com>
---
 drivers/vhost/vsock.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index b69c260eaeff..9142fa1143b2 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -869,6 +869,7 @@ static int vhost_vsock_set_features(struct vhost_vsock *vsock, u64 features)
 	    vsock->dev.iotlb)
 		vhost_clear_device_iotlb(&vsock->dev);
 
-	if ((features & (1ULL << VIRTIO_F_ACCESS_PLATFORM))) {
+	if ((features & (1ULL << VIRTIO_F_ACCESS_PLATFORM)) &&
+	    !vsock->dev.iotlb) {
 		if (vhost_init_device_iotlb(&vsock->dev))
 			goto err;
-- 
2.34.1

Re: [PATCH v4 3/3] vhost/vsock: keep IOTLB across feature updates

[Stefano Garzarella]

On Fri, Aug 14, 2026 at 03:29:03PM +0800, Jia Jia wrote:
>VHOST_SET_FEATURES is also used to update logging while a device is
>running. When ACCESS_PLATFORM stays enabled, allocating a new empty
>IOTLB on every call drops valid translations and forces avoidable
>misses.
>
>Initialize the device IOTLB only when one does not already exist.
>
>Fixes: e13a6915a03f ("vhost/vsock: add IOTLB API support")
>Signed-off-by: Jia Jia <physicalmtea@gmail.com>
>---
> drivers/vhost/vsock.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
>diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>index b69c260eaeff..9142fa1143b2 100644
>--- a/drivers/vhost/vsock.c
>+++ b/drivers/vhost/vsock.c
>@@ -869,6 +869,7 @@ static int vhost_vsock_set_features(struct vhost_vsock *vsock, u64 features)
> 	    vsock->dev.iotlb)
> 		vhost_clear_device_iotlb(&vsock->dev);
>

Ah, okay, now I see why you did it in the other patch, but if we move 
dev.iotlb checks in the functions we can still do that.

>-	if ((features & (1ULL << VIRTIO_F_ACCESS_PLATFORM))) {
>+	if ((features & (1ULL << VIRTIO_F_ACCESS_PLATFORM)) &&
>+	    !vsock->dev.iotlb) {
> 		if (vhost_init_device_iotlb(&vsock->dev))

IIUC vhost_init_device_iotlb() handles the case where dev.iotlb is 
already initialized and override it. Here we are preventing that.

Will we do the same in vhost-net? If yes, all the callers will call 
vhost_init_device_iotlb() with `dev.iotlb` NULL, so should we remove 
that behaviour and add the check we are adding here inside the 
vhost_init_device_iotlb()?

Or there is an use case where vhost_init_device_iotlb() is called with 
an already initialized dev.iotlb ?

Thanks,
Stefano

> 			goto err;
>-- 
>2.34.1
>

Re: [PATCH v4 0/3] vhost/vsock: fix device IOTLB feature lifecycle

[Stefano Garzarella]

On Fri, Aug 14, 2026 at 03:29:00PM +0800, Jia Jia wrote:
>vhost-vsock leaves the device IOTLB attached when userspace clears
>VIRTIO_F_ACCESS_PLATFORM. It also replaces an existing IOTLB with an
>empty one whenever a later feature update keeps ACCESS_PLATFORM enabled.
>
>Patch 1 adds a common vhost helper that detaches the device IOTLB from
>all virtqueues, clears their metadata caches, drops queued IOTLB miss
>messages, and frees the old table after all virtqueues have released
>their pointers.

In the v3 you mentioned that this could be used also in vhost-net and 
maybe vhost-scsi. Would it be better to include the other patches in 
this series as well, since we're basically fixing the same issues, or 
have they already been merged?

Thanks,
Stefano

>
>Patch 2 uses the helper when vhost-vsock clears ACCESS_PLATFORM. The
>acked_features update remains in the vhost-vsock-specific loop.
>
>Patch 3 avoids replacing an existing IOTLB when ACCESS_PLATFORM remains
>enabled across a feature update.
>
>Changes since v3:
>- move the IOTLB teardown helper from vhost-vsock into common vhost code
>- keep acked_features updates in the backend-specific loop
>- add the common helper as a separate first patch
>
>Jia Jia (3):
>  vhost: add helper to clear device IOTLB
>  vhost/vsock: discard IOTLB when ACCESS_PLATFORM is cleared
>  vhost/vsock: keep IOTLB across feature updates
>
> drivers/vhost/vhost.c | 24 ++++++++++++++++++++++++
> drivers/vhost/vhost.h |  1 +
> drivers/vhost/vsock.c |  7 ++++++-
> 3 files changed, 31 insertions(+), 1 deletion(-)
>
>-- 
>2.34.1
>