Re: [PATCH RESEND v18 07/12] PCI/TPH: Add pcie_tph_supported() helper to check TPH capability attributes

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The `pcie_tph_supported()` helper ignores the system-wide `pci_tph_disabled` flag, causing VFIO to incorrectly expose an unusable TPH capability to guests.
--

commit 8a6b48383e4674ff26e8119bccd07a94e9e6b180
Author: Chengwen Feng <fengchengwen@huawei.com>

PCI/TPH: Add pcie_tph_supported() helper to check TPH capability attributes

This commit adds the pcie_tph_supported() helper to check if a PCI device
has a valid TPH capability or Extended TPH support. The helper is intended
for use by VFIO to query TPH existence and capabilities uniformly.

> diff --git a/drivers/pci/tph.c b/drivers/pci/tph.c
> --- a/drivers/pci/tph.c
> +++ b/drivers/pci/tph.c

[ ... ]

> @@ -596,3 +596,22 @@ void pci_tph_init(struct pci_dev *pdev)
>  	save_size = sizeof(u32) + num_entries * sizeof(u16);
>  	pci_add_ext_cap_save_buffer(pdev, PCI_EXT_CAP_ID_TPH, save_size);
>  }

[ ... ]

> +/**
> + * pcie_tph_supported - Check TPH capability attribute
> + * @pdev: PCI device to query
> + * @want_ext: false - check TPH cap exists; true - check EXT_TPH support
> + *
> + * Return: true on matched condition, false otherwise
> + */
> +bool pcie_tph_supported(struct pci_dev *pdev, bool want_ext)
> +{
> +	if (!pdev->tph_cap)
> +		return false;
> +

[Severity: Medium]
Should this function also check the system-wide pci_tph_disabled flag?

If the host administrator explicitly disables TPH via the notph boot
parameter, pci_tph_disabled is set to true. Because this helper only
checks pdev->tph_cap, it appears VFIO will still evaluate this as true
and expose a "zombie" TPH capability to guests.

The guest would see the capability but silently fail to enable it since
VFIO's configuration intercept correctly enforces pci_tph_disabled.

Would it be better to return false here if pci_tph_disabled is set, so
we respect the administrator's global disable intent and avoid exposing
unusable capabilities to guests?

> +	if (!want_ext)
> +		return true;
> +
> +	return pdev->tph_ext_support;
> +}
> +EXPORT_SYMBOL(pcie_tph_supported);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260623085048.51139-1-fengchengwen@huawei.com?part=7