Re: [PATCH v7 08/20] KVM: selftests: Add helper to get host IRQ from device MSI-X for IRQ bypass test

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Reading /proc/interrupts with a fixed 4096-byte buffer truncates lines on large machines, leading to incorrect IRQ numbers or test crashes.
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commit 399b5fbbf0a019bffe136ff08d75cf31f2c2655f
Author: David Matlack <dmatlack@google.com>

KVM: selftests: Add helper to get host IRQ from device MSI-X for IRQ bypass test

This commit introduces proc_util.c and vfio_msix_to_host_irq() to parse
/proc/interrupts and retrieve the host Linux IRQ for a given VFIO device BDF
and MSI-X vector. The helper is intended to be used by the eventfd IRQ test.

[ ... ]
> diff --git a/tools/testing/selftests/kvm/lib/proc_util.c b/tools/testing/selftests/kvm/lib/proc_util.c
> new file mode 100644
> index 0000000000000..84d30f055a0a9
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/lib/proc_util.c
[ ... ]
> +unsigned int vfio_msix_to_host_irq(const char *device_bdf, int msix)
> +{
> +	char search_string[64];
> +	char line[4096];
> +	int irq = -1;
> +	FILE *fp;
> +
> +	fp = open_proc_interrupts();
> +
> +	snprintf(search_string, sizeof(search_string), "vfio-msix[%d]", msix);
> +
> +	while (fgets(line, sizeof(line), fp)) {
> +		if (strstr(line, device_bdf) && strstr(line, search_string)) {
> +			TEST_ASSERT_EQ(1, sscanf(line, "%d:", &irq));

[Severity: Medium]
Does this 4096-byte buffer accommodate lines from /proc/interrupts on hosts
with a large number of CPUs?

If a host has enough CPUs to push a single line beyond 4096 bytes, fgets()
will split the line across multiple reads.

If the target device strings happen to fall into a subsequent chunk, could
sscanf() mistakenly parse a CPU interrupt count as the host IRQ, or fail
entirely and trigger the assert?

> +			break;
> +		}
> +	}
> +
> +	fclose(fp);
> +
> +	TEST_ASSERT(irq != -1, "Failed to locate IRQ for %s %s", device_bdf,
> +		    search_string);
> +	return (unsigned int)irq;
> +}

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Sashiko AI review · https://sashiko.dev/#/patchset/20260613002031.745413-1-seanjc@google.com?part=8