Re: [PATCH v2 2/4] vfio: selftests: Introduce vfio_dma_mapping_perf_test

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Medium] The `TIME` macro can clobber `errno` before the caller evaluates it.
- [Low] Diagnostic output uses `printf` instead of `TH_LOG` or `ksft_print_msg`, violating the Test Anything Protocol (TAP) format.
--

--- Patch [2]: [PATCH v2 2/4] vfio: selftests: Introduce vfio_dma_mapping_perf_test ---
commit 3d215ae55639b2f45faac3bfc752e16beff09489
Author: Aaron Lewis <aaronlewis@google.com>

vfio: selftests: Introduce vfio_dma_mapping_perf_test
    
Introduce vfio_dma_mapping_perf_test to aid in latency testing. Rather
than a traditional pass/fail test, which tends to be flaky when
enforcing latency bounds, this test directly reports the latency of
various stages in the mapping and unmapping process.

> diff --git a/tools/testing/selftests/vfio/lib/include/libvfio.h b/tools/testing/selftests/vfio/lib/include/libvfio.h
> index 07862b470777b..cf322b499cfba 100644
> --- a/tools/testing/selftests/vfio/lib/include/libvfio.h
> +++ b/tools/testing/selftests/vfio/lib/include/libvfio.h

[ ... ]

> @@ -9,6 +9,34 @@
>  #include <libvfio/vfio_pci_device.h>
>  #include <libvfio/vfio_pci_driver.h>
>  
> +#include <stdint.h>
> +#include <time.h>
> +#include <linux/time64.h>

[ ... ]

> +static inline uint64_t timer_elapsed_ns(struct timespec start)
> +{
> +	struct timespec end;
> +
> +	clock_gettime(CLOCK_MONOTONIC, &end);
> +
> +	return (uint64_t)(end.tv_sec - start.tv_sec) * NSEC_PER_SEC +
> +	       (uint64_t)(end.tv_nsec - start.tv_nsec);
> +}
> +
> +#define TIME(_name, _expression) do {				   \
> +	struct timespec __start;				   \
> +								   \
> +	timer_start(&__start);					   \
> +	_expression;						   \
> +	printf(_name " = %.2lfms\n",				   \

[Severity: Medium]
Can this TIME macro clobber errno before the caller evaluates it?

If the target _expression (like mmap) fails and sets errno, the macro then
calls clock_gettime() inside timer_elapsed_ns() and printf(). These libc
functions can modify errno, causing the caller to read an incorrect errno
value.

For example, this happens in dma_map_unmap(), where the SKIP() check reads
errno after mmap() is executed through this macro:

tools/testing/selftests/vfio/vfio_dma_mapping_perf_test.c:dma_map_unmap() {
    ...
    TIME("mmap",
         region.vaddr = mmap(NULL, size, PROT_READ | PROT_WRITE, flags, -1, 0));

    /* Skip the test if there aren't enough HugeTLB pages available. */
    if (flags & MAP_HUGETLB && region.vaddr == MAP_FAILED)
        SKIP(return, "mmap() failed: %s (%d)\n", strerror(errno), errno);
    ...
}


[Severity: Low]
Does this output violate the Test Anything Protocol (TAP) format?

Since it outputs directly to stdout without the TAP diagnostic prefix
("# "), it might confuse TAP parsers. Would it be better to use TH_LOG() or
ksft_print_msg() here?

> +	       (double)timer_elapsed_ns(__start) / NSEC_PER_MSEC); \
> +} while (0)
> +

> diff --git a/tools/testing/selftests/vfio/vfio_dma_mapping_perf_test.c b/tools/testing/selftests/vfio/vfio_dma_mapping_perf_test.c
> new file mode 100644
> index 0000000000000..26c04cabef616
> --- /dev/null
> +++ b/tools/testing/selftests/vfio/vfio_dma_mapping_perf_test.c

[ ... ]

> +TEST_F(vfio_dma_mapping_perf_test, dma_map_unmap)
> +{
> +	const u64 size = SZ_1G;
> +	const int flags = variant->mmap_flags;
> +	struct dma_region region;
> +
> +	printf("mmap size = %lluG\n", (unsigned long long)(size / SZ_1G));

[Severity: Low]
Similar to the TIME macro above, does this directly output to stdout without
the TAP diagnostic prefix?

Using ksft_print_msg() or TH_LOG() instead would ensure the diagnostic output
complies with the TAP specification.

> +
> +	TIME("mmap",
> +	     region.vaddr = mmap(NULL, size, PROT_READ | PROT_WRITE, flags, -1, 0));
> +

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260804165748.1060476-1-aaronlewis@google.com?part=2