Re: [PATCH 4.9 13/20] x86/speculation/mmio: Add mitigation for Processor MMIO Stale Data

On 6/22/22 04:48, Pavel Machek wrote:

Hi!

...

+static int __init mmio_stale_data_parse_cmdline(char *str) +{

• if (!boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA))

• return 0;
  

• if (!str)

• return -EINVAL;
  

• if (!strcmp(str, "off")) {

• mmio_mitigation = MMIO_MITIGATION_OFF;
  

• } else if (!strcmp(str, "full")) {

• mmio_mitigation = MMIO_MITIGATION_VERW;
  

• } else if (!strcmp(str, "full,nosmt")) {

• mmio_mitigation = MMIO_MITIGATION_VERW;
  

• mmio_nosmt = true;
  

• }
• return 0;

+}

This is wrong, AFAICT. Returning 0 will pollute init's environment; Randy was cleaning those lately and we are even seeing them in -stable. See for example b793a01000122d2bd133ba451a76cc135b5e162c.

The early return 0 should disappear, too; we should validate the option even on non-buggy machines.

It's good to be on the lookout for such problems, but __setup() functions (like I was cleaning) are the opposite (sad:( of early_param() functions, which this one is.

early_param() does return 0 on success and non-zero on error, so this looks OK to me.