Messages in this thread |  | | Date | Sun, 7 Jan 2018 09:20:26 +0100 | From | Greg KH <> | Subject | Re: [PATCH v2 4/8] x86/spec_ctrl: Add sysctl knobs to enable/disable SPEC_CTRL feature |
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On Sat, Jan 06, 2018 at 04:25:19PM -0500, Konrad Rzeszutek Wilk wrote: > On Sat, Jan 06, 2018 at 10:10:59AM -0800, Tim Chen wrote: > > > > > > On 01/06/2018 12:54 AM, Greg KH wrote: > > > On Fri, Jan 05, 2018 at 06:12:19PM -0800, Tim Chen wrote: > > >> From: Tim Chen <tim.c.chen@linux.intel.com> > > >> From: Andrea Arcangeli <aarcange@redhat.com> > > >> > > >> There are 2 ways to control IBRS > > >> > > >> 1. At boot time > > >> noibrs kernel boot parameter will disable IBRS usage > > >> > > >> Otherwise if the above parameters are not specified, the system > > >> will enable ibrs and ibpb usage if the cpu supports it. > > >> > > >> 2. At run time > > >> echo 0 > /sys/kernel/debug/x86/ibrs_enabled will turn off IBRS > > >> echo 1 > /sys/kernel/debug/x86/ibrs_enabled will turn on IBRS in kernel > > >> echo 2 > /sys/kernel/debug/x86/ibrs_enabled will turn on IBRS in both userspace and kernel > > >> > > > This is going to create headaches in the future. > > That is future CPUs there will be no need for this MSR nor retpoline as > the CPUs will observe correctness when switching .. rings/vm-exits/etc > and I would assume that 'ibrs_enabled' will return 0. > > And that will make folks scared and run to support/Intel with > complaints. > > Furthmore with the 'retpoline' work you can disable IBRS and instead use > 'retpoline's as mitigation - and again the 'ibrs_enabled' is now zero. > Cue in horde of customers calling support. > > Would it be better to have an global /sys/../spectre_resistent instead > of these 'well, check if the repoline sysfs is enabled, or if that is > not, then look at the cpuid flags'. > > It would be good to have this future proof.
It's a debugfs api, it can be changed at any time, to be anything we want, and all is fine :)
Let's get this all working first please, and then a "real" api can be designed and implemented to please everyone.
thanks,
greg k-h
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