Re: [PATCH v2.1] x86/retpoline: Fill return stack buffer on vmexit

[David Woodhouse]

On Thu, 2018-01-11 at 10:22 -0500, Brian Gerst wrote:
> On Thu, Jan 11, 2018 at 9:32 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > On Thu, Jan 11, 2018 at 02:28:32PM +0000, David Woodhouse wrote:
> >> On Thu, 2018-01-11 at 08:20 -0600, Josh Poimboeuf wrote:
> >> >
> >> > This seems weird. I liked v1 a lot better. What's the problem with
> >> > patching in the whole thing?
> >> >
> >> > Also, if you go back to v1, it should be an easy objtool fix, just add
> >> > ANNOTATE_NOSPEC_ALTERNATIVE in front of it.
> >>
> >> The objection was that I was patching in a fairly long set of
> >> instructions. I confess I don't actually know why that's a problem,
> >
> > You get a giant string of NOPs, a single jmp should be faster.
> 
> That could be handled in add_nops(), where if over a certain threshold
> it changes to a JMP.

Currently that only processes the *altinstr* doesn't it? Not the
oldinstr?

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