Re: [PATCH 0/7] IBRS patch series

Andrea Arcangeli
2018-01-05T16:42:50Z

On Fri, Jan 05, 2018 at 04:37:30PM +0000, David Woodhouse wrote:
> You are completely ignoring pre-Skylake here.
>
> On pre-Skylake, retpoline is perfectly sufficient and it's a *lot*
> faster than the IBRS option which is almost prohibitively slow.
>
> We didn't do it just for fun. And it's working fine; it isn't *that*
> complex.

How do you enable IBRS when the CPU switches to SMM?

Do you already have this 2-way code emission from gcc and patching
with a 3-way alternatives at boot between ibrs and 2 reptoline version
emitted by gcc and alternatives between ibrs and ibpb where SPEC_CTRL
is missing on some CPU but IBPB_SUPPORT is available?

Or are you talking about having done this on a non upstream Xen build
only without the 2-way code emission for gcc?