Re: [PATCH v3 1/3] riscv: hwprobe: initialize pair->value in hwprobe_one_pair()

On Fri, Jul 24, 2026 at 9:14 PM Andy Chiu <[email protected]> wrote:
>
> The vendor-extension handlers reached from hwprobe_one_pair()
> (hwprobe_isa_vendor_ext_thead_0() and friends) only OR the present bits
> into pair->value via VENDOR_EXTENSION_SUPPORTED() and clear their own
> missing bits; they assume the caller has already zeroed pair->value.
>
> That holds for hwprobe_get_values() (it zeroes each pair) and
> hwprobe_get_cpus() (it re-initializes its scratch pair per key), but not
> for complete_hwprobe_vdso_data(), which reuses a single pair across all
> keys

For loop moment LOL

> without re-zeroing. A vendor key therefore inherits stale bits from
> the previously probed key, and the wrong value is cached in the vDSO
> all_cpu_hwprobe_values[] and handed to userspace on the fast patih.
>
> Zero pair->value once at the top of hwprobe_one_pair() so every handler
> starts from a clean value regardless of the caller, and drop the now
> redundant zeroing in the *_BLOCK_SIZE cases. hwprobe_isa_ext0() keeps its
> own zeroing because hwprobe_ext0_has() calls it directly, bypassing
> hwprobe_one_pair().
>
> Fixes: a5ea53da65c5 ("riscv: hwprobe: Add thead vendor extension probing")
> Signed-off-by: Andy Chiu <[email protected]>

 Reviewed-by: Jesse Taube <[email protected]>


> ---
> Changelog v3:
>  - new patch since v3
> ---
>  arch/riscv/kernel/sys_hwprobe.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
> index caf6762427c8..d2bb70fed8b9 100644
> --- a/arch/riscv/kernel/sys_hwprobe.c
> +++ b/arch/riscv/kernel/sys_hwprobe.c
> @@ -295,6 +295,8 @@ static u64 hwprobe_vec_misaligned(const struct cpumask *cpus)
>  static void hwprobe_one_pair(struct riscv_hwprobe *pair,
>                              const struct cpumask *cpus)
>  {
> +       pair->value = 0;
> +
>         switch (pair->key) {
>         case RISCV_HWPROBE_KEY_MVENDORID:
>         case RISCV_HWPROBE_KEY_MARCHID:
> @@ -329,17 +331,14 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair,
>                 break;
>
>         case RISCV_HWPROBE_KEY_ZICBOZ_BLOCK_SIZE:
> -               pair->value = 0;
>                 if (hwprobe_ext0_has(cpus, RISCV_HWPROBE_EXT_ZICBOZ))
>                         pair->value = riscv_cboz_block_size;
>                 break;
>         case RISCV_HWPROBE_KEY_ZICBOM_BLOCK_SIZE:
> -               pair->value = 0;
>                 if (hwprobe_ext0_has(cpus, RISCV_HWPROBE_EXT_ZICBOM))
>                         pair->value = riscv_cbom_block_size;
>                 break;
>         case RISCV_HWPROBE_KEY_ZICBOP_BLOCK_SIZE:
> -               pair->value = 0;
>                 if (hwprobe_ext0_has(cpus, RISCV_HWPROBE_EXT_ZICBOP))
>                         pair->value = riscv_cbop_block_size;
>                 break;
> --
> 2.43.0
>
>
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>


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