On Fri, Feb 23, 2018 at 06:35:30PM +0100, Paolo Bonzini wrote:
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).
Right. PVH is HVM without any emulated devices or BIOSes or such.
In the context of the paravirt ops, Xen PVH == Xen HVM.
Xen PV (and lguests) are the only ones that patch the the callq *0xffffblah
to callq 0xffff800
While everyone else does the wrmsr.
Paolo