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

[David Woodhouse]

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 @@
> Â
> Âvoid __init check_bugs(void)
> Â{
> +#ifdef CONFIG_X86_32
> +ÂÂÂÂÂÂÂ/*
> +ÂÂÂÂÂÂÂ * Regardless of whether PCID is enumerated, the SDM says
> +ÂÂÂÂÂÂÂ * that it can't be enabled in 32-bit mode.
> +ÂÂÂÂÂÂÂ */
> +ÂÂÂÂÂÂÂsetup_clear_cpu_cap(X86_FEATURE_PCID);
> +#endif
> +
> ÂÂÂÂÂÂÂÂidentify_boot_cpu();
> Â#ifndef CONFIG_SMP
> ÂÂÂÂÂÂÂÂpr_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-pickingÂ62a67e123e ("x86/cpu: Merge bugs.c and bugs_64.c").

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