Re: [PATCH v15 14/16] PCI/CXL: Expose CXL Reset as a PCI reset method

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] pci/cxl: incorrect capability probing in cxl_reset_function()
--

commit caffe4423e688e1f05bdb2a57599ac06d181265a
Author: Srirangan Madhavan <smadhavan@nvidia.com>

PCI/CXL: Expose CXL Reset as a PCI reset method

Register cxl_reset with the PCI reset-method interface and place it before
FLR, which does not reset CXL.cache or CXL.mem protocol state.

Return -ENOTTY when device capabilities, function scope, cached HDM state,
or required cache synchronization do not permit a safe reset.

> diff --git a/drivers/pci/cxl.c b/drivers/pci/cxl.c
> index 4c6b712ed4faf..7a225e215ca5c 100644
> --- a/drivers/pci/cxl.c
> +++ b/drivers/pci/cxl.c
[ ... ]
> @@ -651,9 +651,9 @@ int cxl_reset_function(struct pci_dev *pdev, bool probe)
>  
>  	rc = pci_read_config_word(pdev, dvsec + PCI_DVSEC_CXL_CTRL, &ctrl);
>  	if (rc)
> -		return pcibios_err_to_errno(rc);
> +		return probe ? -ENOTTY : pcibios_err_to_errno(rc);
>  	if (PCI_POSSIBLE_ERROR(ctrl))
> -		return -ENODEV;
> +		return probe ? -ENOTTY : -ENODEV;
>  	if (!(ctrl & PCI_DVSEC_CXL_CACHE_ENABLE) ||
>  	    !(ctrl & PCI_DVSEC_CXL_MEM_ENABLE))
>  		return -ENOTTY;

[Severity: Medium]
Will this dynamic state check introduce a regression where the probe incorrectly
fails?

If the BIOS hasn't pre-enabled CXL memory, PCI_DVSEC_CXL_MEM_ENABLE will be 0.
Since this dynamic state is checked before the early return for probe further
down in the function, the method fails probing and isn't registered in sysfs,
even though the OS driver will enable CXL memory later.

Additionally, because the early return happens before static capability checks
like this:

    if (probe)
        return 0;

    /* ... */

    if (!cpu_cache_has_invalidate_memregion())
        return -ENOTTY;

Will this cause a regression that falsely advertises the capability in sysfs on
architectures lacking cache invalidation since the static check is skipped
during probe?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261011021422.3428136-1-smadhavan@nvidia.com?part=14