Re: [PATCH 09/11] x86/pti: enable global pages for shared areas

[Nadav Amit]

Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> wrote:

> 
> From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> 
> The entry/exit text and cpu_entry_area are mapped into userspace and
> the kernel.  But, they are not _PAGE_GLOBAL.  This creates unnecessary
> TLB misses.
> 
> Add the _PAGE_GLOBAL flag for these areas.
> 
> static void __init
> diff -puN arch/x86/mm/pti.c~kpti-why-no-global arch/x86/mm/pti.c
> --- a/arch/x86/mm/pti.c~kpti-why-no-global	2018-03-21 16:32:00.799192311 -0700
> +++ b/arch/x86/mm/pti.c	2018-03-21 16:32:00.803192311 -0700
> @@ -300,6 +300,13 @@ pti_clone_pmds(unsigned long start, unsi
> 			return;
> 
> 		/*
> +		 * Setting 'target_pmd' below creates a mapping in both
> +		 * the user and kernel page tables.  It is effectively
> +		 * global, so set it as global in both copies.
> +		 */
> +		*pmd = pmd_set_flags(*pmd, _PAGE_GLOBAL);
if (boot_cpu_has(X86_FEATURE_PGE)) ?