Re: [PATCH v19 17/18] vfio/pci: Reset hardware TPH state on device enable/disable

[Alex Williamson <alex@shazbot.org>]

On Thu, 2 Jul 2026 20:42:23 +0800
Chengwen Feng <fengchengwen@huawei.com> wrote:

> VFIO allows user space to enable and modify PCI TPH state, but device
> reset only clears hardware TPH registers, while the software TPH state
> maintained in pci/tph.c remains stale.

It's saved and restored, why is it "stale"?  It seems more that the
interface simply doesn't meet our use case.

What about resets through vfio-pci interfaces, should TPH be
automatically disabled?  Thanks,

Alex 

> Fix the stale state leakage by explicitly disabling TPH in core enable
> and disable paths:
> - In vfio_pci_core_enable(), clear leftover TPH state from previous
>   user sessions before device initialization.
> - In vfio_pci_core_disable(), revert any user-modified TPH state
>   when releasing the device.
> 
> This ensures consistent TPH hardware and software state for each
> user session and avoids residual state contamination.
> 
> Signed-off-by: Chengwen Feng <fengchengwen@huawei.com>
> ---
>  drivers/vfio/pci/vfio_pci_core.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index 7251e251824a..5a14439d1ccb 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -612,6 +612,8 @@ int vfio_pci_core_enable(struct vfio_pci_core_device *vdev)
>  
>  	vdev->reset_works = !ret;
>  	vdev->tph_permit = false;
> +	/* Reset TPH status on new user session */
> +	pcie_disable_tph(vdev->pdev);
>  	pci_save_state(pdev);
>  	vdev->pci_saved_state = pci_store_saved_state(pdev);
>  	if (!vdev->pci_saved_state)
> @@ -759,6 +761,9 @@ void vfio_pci_core_disable(struct vfio_pci_core_device *vdev)
>  
>  	vfio_pci_zdev_close_device(vdev);
>  
> +	/* Reset TPH status on exit user session */
> +	pcie_disable_tph(vdev->pdev);
> +
>  	/*
>  	 * If we have saved state, restore it.  If we can reset the device,
>  	 * even better.  Resetting with current state seems better than