linux-kernel - Re: [PATCHv4 3/4] x86/boot/compressed/64: Introduce place

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Message-ID: <20171208110722.gl2cxdq2vlg6olih@node.shutemov.name>
Date:   Fri, 8 Dec 2017 14:07:22 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Borislav Petkov <bp@...e.de>, Andi Kleen <ak@...ux.intel.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 3/4] x86/boot/compressed/64: Introduce
 place_trampoline()

On Thu, Dec 07, 2017 at 07:30:48AM +0100, Ingo Molnar wrote:
> > We also need a small stack in the trampoline to re-enable long mode via
> > long return. But stack and code can share the page just fine.
> 
> BTW., I'm not sure this is necessarily a good idea: it means writable+executable 
> memory, which we generally try to avoid. How complicated would it be to have them 
> separate?

It's trivial: you only need to bump TRAMPOLINE_32BIT_SIZE.

But it doesn't make much sense. We're running from indentity mapping: all
memory is r/w without NX bit set (and IA32_EFER.NXE is 0).

-- 
 Kirill A. Shutemov