linux-kernel - Re: [PATCH v3 01/13] x86/retpoline: Add initial retpoline support

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Date:   Sun, 7 Jan 2018 23:06:12 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Borislav Petkov <bp@...e.de>
Cc:     "Woodhouse, David" <dwmw@...zon.co.uk>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tim.c.chen@...ux.intel.com" <tim.c.chen@...ux.intel.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "riel@...hat.com" <riel@...hat.com>,
        "keescook@...gle.com" <keescook@...gle.com>,
        "gnomes@...rguk.ukuu.org.uk" <gnomes@...rguk.ukuu.org.uk>,
        "pjt@...gle.com" <pjt@...gle.com>,
        "dave.hansen@...el.com" <dave.hansen@...el.com>,
        "luto@...capital.net" <luto@...capital.net>,
        "jikos@...nel.org" <jikos@...nel.org>,
        "gregkh@...ux-foundation.org" <gregkh@...ux-foundation.org>
Subject: Re: [PATCH v3 01/13] x86/retpoline: Add initial retpoline support

On Sat, Jan 06, 2018 at 01:30:59AM +0100, Borislav Petkov wrote:
> On Fri, Jan 05, 2018 at 11:08:06AM -0600, Josh Poimboeuf wrote:
> > I seem to recall that we also discussed the need for this for converting
> > pvops to use alternatives, though the "why" is eluding me at the moment.
> 
> Ok, here's something which seems to work in my VM here. I'll continue
> playing with it tomorrow. Josh, if you have some example sequences for
> me to try, send them my way pls.

Here's the use case I had in mind before.  With paravirt,

  ENABLE_INTERRUPTS(CLBR_NONE)

becomes

  push	%rax
  call	*pv_irq_ops.irq_enable
  pop	%rax

and I wanted to apply those instructions with an alternative.  It
doesn't work currently because the 'call' isn't first.

-- 
Josh