linux-kernel - Re: [RFC][PATCH] x86/mm: Sync all vmalloc mappings before text

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Message-ID: <20200429185151.GO13592@hirez.programming.kicks-ass.net>
Date:   Wed, 29 Apr 2020 20:51:51 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     rostedt <rostedt@...dmis.org>, Joerg Roedel <jroedel@...e.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shile Zhang <shile.zhang@...ux.alibaba.com>,
        Andy Lutomirski <luto@...capital.net>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tzvetomir Stoyanov <tz.stoyanov@...il.com>
Subject: Re: [RFC][PATCH] x86/mm: Sync all vmalloc mappings before text_poke()

> > Basically, it's a big bitmask, where each bit represents a possible process
> > id (can be 2 gigs if we allow all positive ints!).
> 
> I think you mean 2 giga-bit, for 256MB worth of memory, right ?
> 
> And AFAIU the PID_MAX_LIMIT is at a maximum of 4 million PIDs in
> include/linux/threads.h, which means 512MB worth of memory for a
> bitmask.

PID space is limited to 30 bits per FUTEX_TID_MASK, still, stupid large
:-)