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

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Message-ID: <20200430121627.682061e2@gandalf.local.home>
Date:   Thu, 30 Apr 2020 12:16:27 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Joerg Roedel <jroedel@...e.de>,
        linux-kernel <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>
Subject: Re: [RFC][PATCH] x86/mm: Sync all vmalloc mappings before
 text_poke()

On Thu, 30 Apr 2020 11:20:15 -0400 (EDT)
Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:

> > The right fix is to call vmalloc_sync_mappings() right after allocating
> > tracing or perf buffers via v[zm]alloc().  
> 
> Either right after allocation, or right before making the vmalloc'd data
> structure visible to the instrumentation. In the case of the pid filter,
> that would be the rcu_assign_pointer() which publishes the new pid filter
> table.
> 
> As long as vmalloc_sync_mappings() is performed somewhere *between* allocation
> and publishing the pointer for instrumentation, it's fine.
> 
> I'll let Steven decide on which approach works best for him.

As stated in the other email, I don't see it having anything to do with
vmalloc, but with the per_cpu() allocation. I'll test this theory out by
not even allocating the pid masks and touching the per cpu data at every
event to see if it crashes.

-- Steve