Re: [PATCH v2 37/59] x86/putuser: Provide room for padding

[Peter Zijlstra]

On Fri, Sep 02, 2022 at 09:43:45AM -0700, Linus Torvalds wrote:
> So I don't hate this patch and it's probably good for consistency, but
> I really think that the retbleed tracking could perhaps be improved to
> let this be all unnecessary.
> 
> The whole return stack depth counting is already not 100% exact, and I
> think we could just make the rule be that we don't track leaf
> functions.
> 
> Why? It's just a off-by-one in the already not exact tracking. And -
> perhaps equally importantly - leaf functions are very very common
> dynamically, and I suspect it's trivial to see them.
> 
> Yes, yes, you could make objtool even smarter and actually do some
> kind of function flow graph thing (and I think some people were
> talking about that with the whole ret counting long long ago), but the
> leaf function thing is the really simple low-hanging fruit case of
> that.

So I did the leaf thing a few weeks ago, and at the time the perf gains
where not worth the complexity.

I can try again :-)