linux-kernel - Re: [PATCH 2/3] x86/mm: introduce __PAGE_KERNEL

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Message-Id: <E0AB2852-C4E0-43D3-ABA7-34117A5516C1@gmail.com>
Date:   Fri, 16 Feb 2018 09:47:49 -0800
From:   Nadav Amit <nadav.amit@...il.com>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, luto@...nel.org,
        torvalds@...ux-foundation.org, keescook@...gle.com,
        hughd@...gle.com, jgross@...e.com, x86@...nel.org
Subject: Re: [PATCH 2/3] x86/mm: introduce __PAGE_KERNEL_GLOBAL

Dave Hansen <dave.hansen@...ux.intel.com> wrote:

> 
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> Kernel mappings are historically _PAGE_GLOBAL.  But, with PTI, we do not
> want them to be _PAGE_GLOBAL.  We currently accomplish this by simply
> clearing _PAGE_GLOBAL from the suppotred mask which ensures it is
> cleansed from many of our PTE construction sites:
> 
>        if (!static_cpu_has(X86_FEATURE_PTI))
> 	                __supported_pte_mask |= _PAGE_GLOBAL;
> 
> But, this also means that we now get *no* opportunity to use global
> pages with PTI, even for data which is shared such as the cpu_entry_area
> and entry/exit text.


Doesn’t this patch change the kernel behavior when the “nopti” parameter is used?