> On Jan 15, 2018, at 12:26 AM, Jon Masters <j...@jonmasters.org> wrote: > >> On 01/12/2018 05:03 PM, Henrique de Moraes Holschuh wrote: >> On Fri, 12 Jan 2018, Andi Kleen wrote: >>>> Skylake still loses if it takes an SMI, right? >>> >>> SMMs are usually rare, especially on servers, and are usually >>> not very predictible, and even if you have >> >> FWIW, a data point: SMIs can be generated on demand by userspace on >> thinkpad laptops, but they will be triggered from within a kernel >> context. I very much doubt this is a rare pattern... > > Sure. Just touch some "legacy" hardware that the vendor emulates in a > nasty SMI handler. It's definitely not acceptable to assume that SMIs > can't be generated under the control of some malicious user code. > > Our numbers on Skylake weren't bad, and there seem to be all kinds of > corner cases, so again, it seems as if IBRS is the safest choice. >
And keep in mind that SMIs generally hit all CPUs at once, making them extra nasty. Can we get firmware vendors to refill the return buffer just before RSM?
