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From:   Nadav Amit <namit@vmware.com>
To:     Dave Hansen <dave.hansen@linux.intel.com>
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Subject: Re: [PATCH 09/11] x86/pti: enable global pages for shared areas
Thread-Topic: [PATCH 09/11] x86/pti: enable global pages for shared areas
Thread-Index: AQHTws71NUJeW1FkN0SdPdI31gfiM6PeMD+A
Date:   Fri, 23 Mar 2018 19:12:50 +0000
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References: <20180323174447.55F35636@viggo.jf.intel.com>
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Dave Hansen <dave.hansen@linux.intel.com> wrote:

>=20
> From: Dave Hansen <dave.hansen@linux.intel.com>
>=20
> 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.
>=20
> Add the _PAGE_GLOBAL flag for these areas.
>=20
> 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;
>=20
> 		/*
> +		 * 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 =3D pmd_set_flags(*pmd, _PAGE_GLOBAL);
if (boot_cpu_has(X86_FEATURE_PGE)) ?