linux-kernel - Re: [PATCH 1/2] x86: mmu.h: move mm_context_t::lock member inside CONFIG_MODIFY_LDT

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Message-ID: <29e830f8-65fe-c2b9-1c3f-4359bdf8ac64@rasmusvillemoes.dk>
Date:   Mon, 7 Oct 2019 10:56:09 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] x86: mmu.h: move mm_context_t::lock member inside
 CONFIG_MODIFY_LDT_SYSCALL

On 28/08/2019 21.38, Rasmus Villemoes wrote:
> The placement of the lock member in mm_context_t suggests that it is
> used to protect the vdso* members, but AFAICT, it is only ever used
> under #ifdef CONFIG_MODIFY_LDT_SYSCALL. So guarding the member by the
> same config option is a cheap way to reduce sizeof(mm_struct) by 32
> bytes (only for !CONFIG_MODIFY_LDT_SYSCALL kernels, of course).

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