On 23/02/2018 18:22, Konrad Rzeszutek Wilk wrote: > On Fri, Feb 23, 2018 at 10:37:49AM +0100, Paolo Bonzini wrote: >> On 22/02/2018 18:07, Konrad Rzeszutek Wilk wrote: >>>> Having a paravirt indirect call in the IBRS restore path is not a >>>> good idea, since we are trying to protect from speculative execution >>>> of bogus indirect branch targets. It is also slower, so use >>>> native_wrmsrl on the vmentry path too. >>> But it gets replaced during patching. As in once the machine boots >>> the assembler changes from: >>> >>> callq *0xfffflbah >>> >>> to >>> wrmsr >>> >>> ? I don't think you need this patch. >> >> Why not be explicit? According to the spec, PRED_CMD and SPEC_CTRL > > Explicit is fine. > > But I would recommend you change the commit message to say so, and > perhaps remove 'It is also slower' - as that is incorrect.
Actually it is faster---that's why I made the change in the first place, though later I noticed > If it is detected to be Xen PV, then yes > it will be a call to a function. But that won't help as Xen PV runs in > ring 3, so it has a whole bunch of other issues. Ok, I wasn't sure about PVH (which runs in ring 0 afair). Paolo