Re: [PATCH v2 4/9] perf/cxl: Accept an overflow interrupt on MSI message number 0

On Wed, 29 Jul 2026 07:55:50 -0700
Dave Jiang <[email protected]> wrote:

> cxl_pmu_probe() rejects the PMU with -EINVAL when info->irq <= 0, but
> info->irq holds the MSI/MSI-X message number the device signals overflow
> on (CXL_PMU_CAP_MSI_N_MSK, a 0-based 4-bit field), with -1 meaning "no
> interrupt support". Message number 0 is valid and pci_irq_vector() takes
> a 0-based index, so a compliant device signalling on the first vector is
> wrongly refused and fails to probe.
> 
> Reject only the no-interrupt case (info->irq < 0), matching the sibling
> CXL mailbox and event IRQ handling.
> 
> Fixes: 5d7107c72796 ("perf: CXL Performance Monitoring Unit driver")
> Reported-by: [email protected]
> Closes: https://sashiko.dev/#/patchset/[email protected]?part=1
> Assisted-by: Claude:claude-opus-4-8
> Signed-off-by: Dave Jiang <[email protected]>

Anyone who puts the PMU on vector 0 is presumably sharing one vector
for everything - which to me sounds unwise.  Still indeed a bug.

Reviewed-by: Jonathan Cameron <[email protected]>

> ---
>  drivers/perf/cxl_pmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/perf/cxl_pmu.c b/drivers/perf/cxl_pmu.c
> index 956da8202551..d1e810601e36 100644
> --- a/drivers/perf/cxl_pmu.c
> +++ b/drivers/perf/cxl_pmu.c
> @@ -876,7 +876,7 @@ static int cxl_pmu_probe(struct device *dev)
>  		.capabilities = PERF_PMU_CAP_NO_EXCLUDE,
>  	};
>  
> -	if (info->irq <= 0)
> +	if (info->irq < 0)
>  		return -EINVAL;
>  
>  	rc = pci_irq_vector(pdev, info->irq);