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

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Message-ID: <947455570.77870.1588263502669.JavaMail.zimbra@efficios.com>
Date:   Thu, 30 Apr 2020 12:18:22 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     rostedt <rostedt@...dmis.org>
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 Apr 30, 2020, at 12:16 PM, rostedt rostedt@...dmis.org wrote:

> 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.

As pointed out in my other email, per-cpu allocation uses vmalloc when
size > PAGE_SIZE.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com