[RFC PATCH 0/1] vfio/pci: Disable sriov on PF device close

[RFC PATCH 0/1] vfio/pci: Disable sriov on PF device close

[Samiullah Khawaja]

When userspace closes a VFIO device file descriptor, the vfio driver
performs a hardware reset on the PCIe device to ensure it is returned to
a clean state. However, if the closed device is an SR-IOV Physical
Function (PF), it may have instantiated Virtual Functions (VFs) that are
actively bound to host kernel drivers (or other vfio instances).

When the PF is hardware-reset via VFIO, it implicitly disrupts SR-IOV
operations at the device level. Because this reset happens without
notifying the core PCI driver model, the kernel drivers bound to the VFs
remain loaded and operate under the assumption that the VF hardware is
still functional.

This creates a state mismatch between the kernel's view of the hardware
and the actual device state. Subsequent attempts by the host OS or bound
drivers to interact with the VFs will fail, leading to unexpected
errors.

Disabling SRIOV before resetting the device avoids this issue by tearing
down the VFs and removing the VF devices.

The fix in this patch only disables SRIOV on PF reset for devices bound
to vfio-pci drivers. But this probably needs a fix for kernel drivers
also, maybe return -EBUSY when SRIOV is enabled?

Looking forward to your feedback on this.

---

CC: bhelgaas@google.com
CC: dmatlack@google.com

Samiullah Khawaja (1):
  vfio/pci: Disable sriov on PF device close

 drivers/vfio/pci/vfio_pci_core.c | 7 +++++++
 1 file changed, 7 insertions(+)


base-commit: 0f6da28aab51b16762ed82e8fdeaa5042da45b08
-- 
2.55.0.629.g250fe7f194-goog

[RFC PATCH 1/1] vfio/pci: Disable sriov on PF device close

[Samiullah Khawaja]

When userspace closes a VFIO device file descriptor, the vfio driver
performs a hardware reset on the PCIe device to ensure it is returned to
a clean state. However, if the closed device is an SR-IOV Physical
Function (PF), it may have instantiated Virtual Functions (VFs) that are
actively bound to host kernel drivers (or other vfio instances).

When the PF is hardware-reset via VFIO, it implicitly disrupts SR-IOV
operations at the device level. Because this reset happens without notifying
the core PCI driver model, the kernel drivers bound to the VFs remain loaded
and operate under the assumption that the VF hardware is still functional.

This creates a state mismatch between the kernel's view of the hardware
and the actual device state. Subsequent attempts by the host OS or bound
drivers to interact with the VFs will fail, leading to unexpected
errors.

Disable SR-IOV on the device prior to issuing the PF reset so that the
VFs can teardown and remove at the software level also.

Signed-off-by: Samiullah Khawaja <skhawaja@google.com>
---
 drivers/vfio/pci/vfio_pci_core.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index a113c55845e1..b36c77eb3c40 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -826,6 +826,13 @@ void vfio_pci_core_close_device(struct vfio_device *core_vdev)
 #if IS_ENABLED(CONFIG_EEH)
 	eeh_dev_release(vdev->pdev);
 #endif
+
+	if (pci_num_vf(vdev->pdev)) {
+		device_lock(&vdev->pdev->dev);
+		vfio_pci_core_sriov_configure(vdev, 0);
+		device_unlock(&vdev->pdev->dev);
+	}
+
 	vfio_pci_dma_buf_cleanup(vdev);
 
 	vfio_pci_core_disable(vdev);
-- 
2.55.0.629.g250fe7f194-goog

RE: [RFC PATCH 1/1] vfio/pci: Disable sriov on PF device close

[Tian, Kevin]

> From: Samiullah Khawaja <skhawaja@google.com>
> Sent: Wednesday, August 5, 2026 8:34 AM
> 
> When userspace closes a VFIO device file descriptor, the vfio driver
> performs a hardware reset on the PCIe device to ensure it is returned to
> a clean state. However, if the closed device is an SR-IOV Physical
> Function (PF), it may have instantiated Virtual Functions (VFs) that are
> actively bound to host kernel drivers (or other vfio instances).
> 
> When the PF is hardware-reset via VFIO, it implicitly disrupts SR-IOV
> operations at the device level. Because this reset happens without notifying
> the core PCI driver model, the kernel drivers bound to the VFs remain loaded
> and operate under the assumption that the VF hardware is still functional.
> 
> This creates a state mismatch between the kernel's view of the hardware
> and the actual device state. Subsequent attempts by the host OS or bound
> drivers to interact with the VFs will fail, leading to unexpected
> errors.
> 
> Disable SR-IOV on the device prior to issuing the PF reset so that the
> VFs can teardown and remove at the software level also.
> 
> Signed-off-by: Samiullah Khawaja <skhawaja@google.com>
> ---
>  drivers/vfio/pci/vfio_pci_core.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index a113c55845e1..b36c77eb3c40 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -826,6 +826,13 @@ void vfio_pci_core_close_device(struct vfio_device
> *core_vdev)
>  #if IS_ENABLED(CONFIG_EEH)
>  	eeh_dev_release(vdev->pdev);
>  #endif
> +
> +	if (pci_num_vf(vdev->pdev)) {
> +		device_lock(&vdev->pdev->dev);
> +		vfio_pci_core_sriov_configure(vdev, 0);
> +		device_unlock(&vdev->pdev->dev);
> +	}
> +

Sashiko reported several locking issues with this change:

https://sashiko.dev/#/patchset/20260805003355.728299-2-skhawaja%40google.com

Actually it is a discouraged usage allowing kernel drivers bound to VFs
which belongs to a PF owned by vfio userspace. 

vfio_pci_bus_notifier prints a warning message upon 
BUS_NOTIFY_BOUND_DRIVER:

	"VF %s bound to driver %s while PF bound to driver %s\n"

Fixing this alone is insufficient to remove that warning...

Re: [RFC PATCH 1/1] vfio/pci: Disable sriov on PF device close

[Samiullah Khawaja]

On Wed, Aug 05, 2026 at 09:34:32AM +0000, Tian, Kevin wrote:
>> From: Samiullah Khawaja <skhawaja@google.com>
>> Sent: Wednesday, August 5, 2026 8:34 AM
>>
>> When userspace closes a VFIO device file descriptor, the vfio driver
>> performs a hardware reset on the PCIe device to ensure it is returned to
>> a clean state. However, if the closed device is an SR-IOV Physical
>> Function (PF), it may have instantiated Virtual Functions (VFs) that are
>> actively bound to host kernel drivers (or other vfio instances).
>>
>> When the PF is hardware-reset via VFIO, it implicitly disrupts SR-IOV
>> operations at the device level. Because this reset happens without notifying
>> the core PCI driver model, the kernel drivers bound to the VFs remain loaded
>> and operate under the assumption that the VF hardware is still functional.
>>
>> This creates a state mismatch between the kernel's view of the hardware
>> and the actual device state. Subsequent attempts by the host OS or bound
>> drivers to interact with the VFs will fail, leading to unexpected
>> errors.
>>
>> Disable SR-IOV on the device prior to issuing the PF reset so that the
>> VFs can teardown and remove at the software level also.
>>
>> Signed-off-by: Samiullah Khawaja <skhawaja@google.com>
>> ---
>>  drivers/vfio/pci/vfio_pci_core.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
>> index a113c55845e1..b36c77eb3c40 100644
>> --- a/drivers/vfio/pci/vfio_pci_core.c
>> +++ b/drivers/vfio/pci/vfio_pci_core.c
>> @@ -826,6 +826,13 @@ void vfio_pci_core_close_device(struct vfio_device
>> *core_vdev)
>>  #if IS_ENABLED(CONFIG_EEH)
>>  	eeh_dev_release(vdev->pdev);
>>  #endif
>> +
>> +	if (pci_num_vf(vdev->pdev)) {
>> +		device_lock(&vdev->pdev->dev);
>> +		vfio_pci_core_sriov_configure(vdev, 0);
>> +		device_unlock(&vdev->pdev->dev);
>> +	}
>> +
>
>Sashiko reported several locking issues with this change:
>
>https://sashiko.dev/#/patchset/20260805003355.728299-2-skhawaja%40google.com
>
>Actually it is a discouraged usage allowing kernel drivers bound to VFs
>which belongs to a PF owned by vfio userspace.

Thanks for the feedback Kevin.

I sent this as an RFC specifically to discuss the right approach for
resolving this issue before fixing the locking issues that sashiko
raised. I will get back to this once the discussion to fix this the
right way concludes in the other thread.

Thanks,
Sami

Re: [RFC PATCH 1/1] vfio/pci: Disable sriov on PF device close

[Alex Williamson]

On Wed,  5 Aug 2026 00:33:55 +0000
Samiullah Khawaja <skhawaja@google.com> wrote:

> When userspace closes a VFIO device file descriptor, the vfio driver
> performs a hardware reset on the PCIe device to ensure it is returned to
> a clean state. However, if the closed device is an SR-IOV Physical
> Function (PF), it may have instantiated Virtual Functions (VFs) that are
> actively bound to host kernel drivers (or other vfio instances).

Wait, what?  We actively try to prevent VFs from a vfio-pci owned PF
from being bound to host drivers other than vfio-pci.  You need to
overwrite the imposed driver_override to make this happen and you're in
a very precarious security model to have the VF owned by a trusted
in-kernel driver while the PF is owned by userspace.
 
> When the PF is hardware-reset via VFIO, it implicitly disrupts SR-IOV
> operations at the device level. Because this reset happens without notifying
> the core PCI driver model, the kernel drivers bound to the VFs remain loaded
> and operate under the assumption that the VF hardware is still functional.

And this is a) why we actively try to prevent VFs from being bound to
native host kernel drivers and b) part of the vf_token negotiation of
trust opt-in that must be performed by userspace drivers of the VFs.
 
> This creates a state mismatch between the kernel's view of the hardware
> and the actual device state. Subsequent attempts by the host OS or bound
> drivers to interact with the VFs will fail, leading to unexpected
> errors.

The described model is not a supported use case, there are fundamental
security issues with a userspace vfio-pci driver owning the PF with VFs
bound to in-kernel drivers.

> Disable SR-IOV on the device prior to issuing the PF reset so that the
> VFs can teardown and remove at the software level also.

The below only accounts for the close reset path, not reset in general.
Also note that the SR-IOV model in vfio-pci does have a path by which a
PF can be re-opened with existing VFs.  Whether that's actually used is
a separate question, but this fundamentally disallows that design.

It's possible there are gaps that closing the PF can interrupt the VFs
and we need to defer a reset until the VFs are closed, but the behavior
here seems counter to the original design, and the use case of
in-kernel VF drivers is certainly counter to that design and guardrails
installed to prevent it.  Thanks,

Alex

> Signed-off-by: Samiullah Khawaja <skhawaja@google.com>
> ---
>  drivers/vfio/pci/vfio_pci_core.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index a113c55845e1..b36c77eb3c40 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -826,6 +826,13 @@ void vfio_pci_core_close_device(struct vfio_device *core_vdev)
>  #if IS_ENABLED(CONFIG_EEH)
>  	eeh_dev_release(vdev->pdev);
>  #endif
> +
> +	if (pci_num_vf(vdev->pdev)) {
> +		device_lock(&vdev->pdev->dev);
> +		vfio_pci_core_sriov_configure(vdev, 0);
> +		device_unlock(&vdev->pdev->dev);
> +	}
> +
>  	vfio_pci_dma_buf_cleanup(vdev);
>  
>  	vfio_pci_core_disable(vdev);

Re: [RFC PATCH 1/1] vfio/pci: Disable sriov on PF device close

[Jason Gunthorpe]

On Wed, Aug 05, 2026 at 09:03:23AM -0600, Alex Williamson wrote:
> On Wed,  5 Aug 2026 00:33:55 +0000
> Samiullah Khawaja <skhawaja@google.com> wrote:
> 
> > When userspace closes a VFIO device file descriptor, the vfio driver
> > performs a hardware reset on the PCIe device to ensure it is returned to
> > a clean state. However, if the closed device is an SR-IOV Physical
> > Function (PF), it may have instantiated Virtual Functions (VFs) that are
> > actively bound to host kernel drivers (or other vfio instances).
> 
> Wait, what?  We actively try to prevent VFs from a vfio-pci owned PF
> from being bound to host drivers other than vfio-pci.  You need to
> overwrite the imposed driver_override to make this happen and you're in
> a very precarious security model to have the VF owned by a trusted
> in-kernel driver while the PF is owned by userspace.

Maybe, it really depends on the device. I can easially see someone
using a device where this would be safe. mlx5 for instance is pretty
OK.

So I don't really mind someone doing this, we should block it and warn
it and so on, but like noiommu and the other vfio insecure modes, why
not give an opt in?

> It's possible there are gaps that closing the PF can interrupt the VFs
> and we need to defer a reset until the VFs are closed, 

Oh definately, when running in a SRIOV mode it is really problematic
for the PF to reset while there are any active VFs. The PF controls a
number of shared items (MMIO, ATS, etc) and when it blips everyone is
at risk of unexpected fairly catastrophic system crashing errors
related to the shared items going away.

So resetting the PF device unconditionally when vfio closes is
definately wrong in principal. I can see it maybe working for simple
systems, especially ones that don't MCE..

I don't think we can skip the PF reset on close because of dev_set
reasons and leave a rouge device for the next user, so the thing looks
somewhat troubled?

Adding the sriov disable here at least makes it defensibly safe, that
we do still clear the PF on close, and we don't take risks that the
active VFs will crash the system during the FLR blip.

Though I understand it was not the original intention, I feel we have
ended up in a strange place with the SRIOV PF feature ..

Jason

Re: [RFC PATCH 1/1] vfio/pci: Disable sriov on PF device close

[Alex Williamson]

On Thu, 6 Aug 2026 16:47:39 -0300
Jason Gunthorpe <jgg@ziepe.ca> wrote:

> On Wed, Aug 05, 2026 at 09:03:23AM -0600, Alex Williamson wrote:
> > On Wed,  5 Aug 2026 00:33:55 +0000
> > Samiullah Khawaja <skhawaja@google.com> wrote:
> >   
> > > When userspace closes a VFIO device file descriptor, the vfio driver
> > > performs a hardware reset on the PCIe device to ensure it is returned to
> > > a clean state. However, if the closed device is an SR-IOV Physical
> > > Function (PF), it may have instantiated Virtual Functions (VFs) that are
> > > actively bound to host kernel drivers (or other vfio instances).  
> > 
> > Wait, what?  We actively try to prevent VFs from a vfio-pci owned PF
> > from being bound to host drivers other than vfio-pci.  You need to
> > overwrite the imposed driver_override to make this happen and you're in
> > a very precarious security model to have the VF owned by a trusted
> > in-kernel driver while the PF is owned by userspace.  
> 
> Maybe, it really depends on the device. I can easially see someone
> using a device where this would be safe. mlx5 for instance is pretty
> OK.
> 
> So I don't really mind someone doing this, we should block it and warn
> it and so on, but like noiommu and the other vfio insecure modes, why
> not give an opt in?

An opt-in to what currently?  We generate a warning, but nothing
actually prevents the re-bind to an in-kernel driver.  Whether that's
sustainable in eliminating this reset gap is yet to be seen.

Binding a VF from a userspace owned PF flips our model on its head in
two important ways.  First is the security inversion.  An in-kernel PF
driver is considered trusted, we absolve ourselves of issues related to
whether the PF has access to VF data or interrupts VF operations and
state through reset.  Second, the vf_token model explicitly defines the
trust and coordination boundaries for the userspace SR-IOV ecosystem.
An in-kernel bound VF lives entirely outside of that boundary.  For
example, one mechanism we might use to prevent an MCE around PF reset
would be to zap VF mappings and invalidate dmabufs.  Reinstatement of
those mappings would require userspace coordination, which the vf_token
model would define as an implementation detail in userspace relative to
vf_token coordination and trust.

So we haven't done anything that explicitly blocks or taints this mode,
yet, but correctly handling reset could be a tipping point.

> > It's possible there are gaps that closing the PF can interrupt the VFs
> > and we need to defer a reset until the VFs are closed,   
> 
> Oh definately, when running in a SRIOV mode it is really problematic
> for the PF to reset while there are any active VFs. The PF controls a
> number of shared items (MMIO, ATS, etc) and when it blips everyone is
> at risk of unexpected fairly catastrophic system crashing errors
> related to the shared items going away.
> 
> So resetting the PF device unconditionally when vfio closes is
> definately wrong in principal. I can see it maybe working for simple
> systems, especially ones that don't MCE..
> 
> I don't think we can skip the PF reset on close because of dev_set
> reasons and leave a rouge device for the next user, so the thing looks
> somewhat troubled?

This is what our vf_token model would handle, if we could use it.
Re-open with VFs in use through vfio-pci requires the vf_token
proof/opt-in.  Re-open with no VFs in use could reset the PF, but we
can't account for VFs bound to in-kernel drivers.
 
> Adding the sriov disable here at least makes it defensibly safe, that
> we do still clear the PF on close, and we don't take risks that the
> active VFs will crash the system during the FLR blip.
> 
> Though I understand it was not the original intention, I feel we have
> ended up in a strange place with the SRIOV PF feature ..

I think we have 3 potential options for PF reset:

 a) All resets are blocked or deferred while SR-IOV is active.

 b) VF mappings are zapped/invalidated at PF reset and require
    coordination to be reinstated.

 c) VFs are torn down on all PF resets.

Option (a) is complex and doesn't look like stable material.  A deferred
reset on .close needs to materialize on .remove or .sriov_configure
(and of course .open), but to allow in-kernel VF drivers we can't rely
on vfio usage counts, or even our vf-token trust boundaries, which is
what leads to the .sriov_configure hook since we need to take advantage
of every opportunity to issue a deferred reset when SR-IOV is not
active when we can only rely on the PF state.

Option (b) is potentially more simple, it implements the blocking of
access on reset in the kernel for enforcement, but defers the
coordination of reinstantiating mappings to userspace, which is really
how the vf_token model is intended to work.  This is incompatible with
in-kernel VF drivers, which I think means tainting on VF unbind from
vfio-pci and those working outside the model would tread carefully.

Option (c) is the more heavy handed approach, it means that a PF driver
cannot fail or exit and re-attach.  We have existing logic that handles
a PF driver re-opening the PF device with active VFs and authenticating
the vf_token (logic also broken by in-kernel VF drivers that bypass the
vf_token mechanics).  There also appears to be significant locking
challenges in this approach, ex. the inversion of getting the device
lock for SR-IOV teardown from the ioctl, config space, and .close
contexts.

I'm open to suggestions, PF resets with live VFs is very much a gap
that I'd like to close in the vfio-pci SR-IOV model.  Thanks,

Alex