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Subject: Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict
 Indirect Branch Speculation
To:     Konrad Rzeszutek Wilk <konrad@darnok.org>
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Cc:     Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Andi Kleen <ak@linux.intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
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        Ingo Molnar <mingo@redhat.com>,
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        "Raj, Ashok" <ashok.raj@intel.com>,
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From:   Dave Hansen <dave.hansen@intel.com>
Message-ID: <536542f0-99eb-742b-9d17-5b06e89ee383@intel.com>
Date:   Sat, 27 Jan 2018 07:55:10 -0800
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On 01/27/2018 05:42 AM, Konrad Rzeszutek Wilk wrote:
> On Fri, Jan 26, 2018 at 07:11:47PM +0000, Hansen, Dave wrote:
>> The need for RSB stuffing in all the various scenarios and what the heck it actually mitigates is freakishly complicated.  I've tried to write it all down in one place: https://goo.gl/pXbvBE
> Thank you for sharing that.
> 
> One question on the third from the top (' RSB Stuff (16) After
> irq/nmi/#PF/...').
> 
> It says that :"Return from interrupt path (more than 16 deep) can empty
> RSB".
> 
> Just to clarify - you mean all the returns ('ret') that are happening after
> we call do_IRQ and the stack unwinds - but before we do an 'iret' correct?

Correct.  The RSB is not used or updated by iret.