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

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Message-ID: <20200430211308.74a994dc@oasis.local.home>
Date:   Thu, 30 Apr 2020 21:13:08 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Joerg Roedel <jroedel@...e.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        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>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [RFC][PATCH] x86/mm: Sync all vmalloc mappings before
 text_poke()


[ Joerg, sending again this time not just to you. (hit reply to sender
  and not reply to all). Feel free to resend what you wrote before to this ]

On Thu, 30 Apr 2020 21:14:34 +0200
Joerg Roedel <jroedel@...e.de> wrote:

> And alloc_percpu() calls down into pcpu_alloc(), which allocates new
> percpu chunks using vmalloc() on x86. And there we are again in the
> vmalloc area.  

So after a vmalloc() is made, should the page tables be synced?

This is a rather subtle bug, and I don't think it should be the caller of
percpu_alloc() that needs to call vmalloc_sync_mappings().

What's your suggestion for a fix?

-- Steve