linux-kernel - Re: [tip:x86/pti] x86/pti: Make sure the user/kernel PTEs match

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Date:   Fri, 9 Feb 2018 15:30:02 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     bp@...en8.de, mingo@...nel.org, linux-kernel@...r.kernel.org,
        mroos@...ux.ee, hpa@...or.com, tglx@...utronix.de,
        thomas.lendacky@....com, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/pti] x86/pti: Make sure the user/kernel PTEs match

On 01/03/2018 08:22 AM, tip-bot for Thomas Gleixner wrote:
> --- a/arch/x86/mm/pti.c
> +++ b/arch/x86/mm/pti.c
> @@ -367,7 +367,8 @@ static void __init pti_setup_espfix64(void)
>  static void __init pti_clone_entry_text(void)
>  {
>  	pti_clone_pmds((unsigned long) __entry_text_start,
> -			(unsigned long) __irqentry_text_end, _PAGE_RW);
> +			(unsigned long) __irqentry_text_end,
> +		       _PAGE_RW | _PAGE_GLOBAL);
>  }

We appear to have lost all of our global bits between this and the
cpu_entry_area itself.  To make K8 happy, shouldn't we just *set*
_PAGE_GLOBAL universally instead of clearing it universally?

Also, don't we want _PAGE_GLOBAL in the cpu_entry_area.c pte setting?  I
think I had this for all the shared user/kernel areas near the end of
the KAISER era, but we appear to have totally nuked it for PTI.