linux-kernel - Re: [PATCH] x86/speculation/mds: Flush store buffer after wake up from sleep

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Message-ID: <alpine.DEB.2.21.1906211916000.5503@nanos.tec.linutronix.de>
Date:   Fri, 21 Jun 2019 19:19:20 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Zhenzhong Duan <zhenzhong.duan@...cle.com>
cc:     linux-kernel@...r.kernel.org, mingo@...nel.org, bp@...en8.de,
        x86@...nel.org, hpa@...or.com, jgross@...e.com,
        ndesaulniers@...gle.com, gregkh@...uxfoundation.org,
        srinivas.eeda@...cle.com
Subject: Re: [PATCH] x86/speculation/mds: Flush store buffer after wake up
 from sleep

On Wed, 19 Jun 2019, Zhenzhong Duan wrote:

> Intel document says: "When a thread wakes from a sleep state, the store
> buffer is repartitioned again. This causes the store buffer to transfer
> store buffer entries from the thread that was already active to the one
> which just woke up."
> 
> To avoid data leak from sibling thread to the woken thread, flush store
> buffer right after wake up.

That's a pointless exercise. The buffers are flushed again when returning
to user space. Inside the kernel the potential leak is completely
uninteresting unless you consider the kernel as a malicious entity.
 
> Move mds_idle_clear_cpu_buffers() after trace_hardirqs_on() to ensure
> all store buffer entries are flushed before sleep.

I'm fine with that change, albeit trace_hardirqs_on() is hardly leaking
somethimg interesting.

Thanks,

	tglx