Re: [PATCH 4.4 29/63] x86/mm: Disable PCID on 32-bit kernels

David Woodhouse
2018-01-09T16:05:57Z

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On Mon, 2018-01-01 at 15:24 +0100, Greg Kroah-Hartman wrote:
>
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -19,6 +19,14 @@
>
>  void __init check_bugs(void)
>  {
> +#ifdef CONFIG_X86_32
> +       /*
> +        * Regardless of whether PCID is enumerated, the SDM says
> +        * that it can't be enabled in 32-bit mode.
> +        */
> +       setup_clear_cpu_cap(X86_FEATURE_PCID);
> +#endif
> +
>         identify_boot_cpu();
>  #ifndef CONFIG_SMP
>         pr_info("CPU: ");
>

Razvan points out that the #ifdef there is redundant; in older kernels,
bugs.c is only built on 32-bit anyway.

We're working on backporting the other CPU_BUG_* and sysfs
vulnerabilities bits to 4.9 (first), and will probably end up
cherry-picking 62a67e123e ("x86/cpu: Merge bugs.c and bugs_64.c").

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