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Subject: Re: [PATCH] x86/speculation: Use Indirect Branch Prediction Barrier
 in context switch
To:     Borislav Petkov <bp@alien8.de>
Cc:     David Woodhouse <dwmw@amazon.co.uk>, arjan@linux.intel.com,
        tglx@linutronix.de, karahmed@amazon.de, x86@kernel.org,
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        pbonzini@redhat.com, ak@linux.intel.com,
        torvalds@linux-foundation.org, gregkh@linux-foundation.org,
        mingo@kernel.org, luto@kernel.org, linux@dominikbrodowski.net
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 <20180130215731.pszc5u4gcc32ds4v@pd.tnic>
From:   Tim Chen <tim.c.chen@linux.intel.com>
Message-ID: <296de30b-515b-6eab-1b13-bb2f71451004@linux.intel.com>
Date:   Tue, 30 Jan 2018 14:26:53 -0800
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On 01/30/2018 01:57 PM, Borislav Petkov wrote:
> On Tue, Jan 30, 2018 at 01:03:20PM -0800, Tim Chen wrote:
>> So it doesn't seem to be very practical attack if the victim has set
>> itself to be non-dumpable.
> 
> Probably, but considering how cheap our fix is, we might just as well
> plug that hole too.
> 

If the process has multiple threads running on different cpus,
you will need to set IBPB on all cpus they are running in
order to achieve your purpose.  So it is not necessarily cheap.
But I don't think it is really necessary.

Tim