linux-kernel - Re: [PATCH v4 7/7] x86/speculation: Add basic IBPB (Indirect Branch Prediction Barrier) support

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Message-ID: <1516882315.30244.88.camel@infradead.org>
Date:   Thu, 25 Jan 2018 12:11:55 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     arjan@...ux.intel.com, tglx@...utronix.de, karahmed@...zon.de,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        tim.c.chen@...ux.intel.com, peterz@...radead.org,
        pbonzini@...hat.com, ak@...ux.intel.com,
        torvalds@...ux-foundation.org, gregkh@...ux-foundation.org,
        dave.hansen@...el.com, gnomes@...rguk.ukuu.org.uk,
        ashok.raj@...el.com, mingo@...nel.org
Subject: Re: [PATCH v4 7/7] x86/speculation: Add basic IBPB (Indirect
 Branch Prediction Barrier) support

On Thu, 2018-01-25 at 13:03 +0100, Borislav Petkov wrote:
> On Thu, Jan 25, 2018 at 11:58:20AM +0000, David Woodhouse wrote:
> > They're immediates, not registers. So it's like the first example
> in...
> 
> Oh, I know very well what they are - I simply find the macro more
> readable if there are less or no arguments.

Oh, I agree, but having to write 0x49 there instead of
MSR_IA32_PRED_CMD was a more pressing reason *not* to change it.

There are possibly macro hacks that can make that work (the first naïve
attempt didn't) but it exceeded my boredom threshold fairly rapidly.

If you send me a version which still uses MSR_IA32_PRED_CMD and
PRED_CMD_IBPB instead of hard-coding the numbers, and which doesn't end
up with piles of __stringify() and similar crap to do so, I'll happily
change it.
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