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

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Date:   Wed, 29 Apr 2020 10:32:16 -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()

On Wed, 29 Apr 2020 16:10:04 +0200
Joerg Roedel <jroedel@...e.de> wrote:

> On Wed, Apr 29, 2020 at 10:07:31AM -0400, Steven Rostedt wrote:
> > Talking with Mathieu about this on IRC, he pointed out that my code does
> > have a vzalloc() that is called:
> > 
> > in trace_pid_write()
> > 
> > 	pid_list->pids = vzalloc((pid_list->pid_max + 7) >> 3);
> > 
> > This is done when -P1,2 is on the trace-cmd command line.  
> 
> Yeah, I was guessing something like this, init_mm has a mapping which
> poking_mm has not. I currently try to reproduce this on one of my
> machines.

Note, in use_temporary_mm(poking_mm), poking_mm only contains the page that
needs to be updated. But will get added to per_cpu(cpu_tlbstate.loaded_mm),
which appears to be the one that's not updated.

-- Steve