Re: [PATCH v3 5/6] x86/alternative: Use a single access in text_poke() where possible

[Sean Christopherson]

On Thu, Jan 10, 2019 at 12:32:43PM -0500, Steven Rostedt wrote:
> On Thu, 10 Jan 2019 11:20:04 -0600
> Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:
> 
> 
> > > While I can't find a reason for hypervisors to emulate this instruction,
> > > smarter people might find ways to turn it into a security exploit.  
> > 
> > Interesting point... but I wonder if it's a realistic concern.  BTW,
> > text_poke_bp() also relies on undocumented behavior.
> 
> But we did get an official OK from Intel that it will work. Took a bit
> of arm twisting to get them to do so, but they did. And it really is
> pretty robust.

Did we (they?) list any caveats for this behavior?  E.g. I'm fairly
certain atomicity guarantees go out the window if WC memtype is used.