linux-kernel - Re: [patch V181 35/54] x86/entry: Align entry text section to PMD boundary

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Message-ID: <alpine.DEB.2.21.1805181232280.2172@nanos.tec.linutronix.de>
Date:   Fri, 18 May 2018 12:38:39 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirsky <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Borislav Petkov <bpetkov@...e.de>,
        Greg KH <gregkh@...uxfoundation.org>, keescook@...gle.com,
        hughd@...gle.com, Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Rik van Riel <riel@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        David Laight <David.Laight@...lab.com>,
        Eduardo Valentin <eduval@...zon.com>, aliguori@...zon.com,
        Will Deacon <will.deacon@....com>,
        Vlastimil Babka <vbabka@...e.cz>, daniel.gruss@...k.tugraz.at,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [patch V181 35/54] x86/entry: Align entry text section to PMD
 boundary

On Thu, 17 May 2018, Josh Poimboeuf wrote:

> On Wed, Dec 20, 2017 at 10:35:38PM +0100, Thomas Gleixner wrote:
> > From: Thomas Gleixner <tglx@...utronix.de>
> > 
> > The (irq)entry text must be visible in the user space page tables. To allow
> > simple PMD based sharing, make the entry text PMD aligned.
> > 
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > Signed-off-by: Ingo Molnar <mingo@...nel.org>
> 
> With my config, this patch adds 2.5M (+~25%) to the kernel text size.
> Is there a more granular way to achieve this?

We could make it PTE granular with some effort, but that would make the
whole PTI handling more complex. So not sure, if that's worth it.

Thanks,

	tglx