On Wed, 2018-01-31 at 11:01 +0100, Peter Zijlstra wrote: > On Tue, Jan 30, 2018 at 09:12:21PM -0600, Josh Poimboeuf wrote: > > > > Or, maybe we should just forget the whole thing and just stick with the > > dynamic IBRS checks with lfence. Yes, it's less ideal for the kernel, > > but adding these acrobatics to objtool also has a cost. > > For now, IBRS seems off the table entirely. But no, I really don't want > to have to unconditionally eat the LFENCE cost in all those sites.
There's also alternatives. And without the IBRS-on-kernel-entry bits there aren't that many call sites that really need this anyway and don't have *other* conditionals that really are runtime-only (like dumpable etc.).
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