Messages in this thread | | | Date | Thu, 21 Feb 2019 10:58:06 -0800 | From | Andi Kleen <> | Subject | Re: [PATCH] x86/fpu: Parse comma separated list passed in clearcpuid |
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On Thu, Feb 21, 2019 at 02:37:45PM +0100, Peter Zijlstra wrote: > On Thu, Feb 21, 2019 at 08:12:25AM -0500, Prarit Bhargava wrote: > > Users cannot disable multiple CPU features with the kernel parameter > > clearcpuid=. For example, "clearcpuid=154 clearcpuid=227" only disables > > CPUID bit 154. > > > > Previous to commit 0c2a3913d6f5 ("x86/fpu: Parse clearcpuid= as early XSAVE > > argument") it was possible to pass multiple clearcpuid options as kernel > > parameters using individual entries. With the new code it isn't easy to > > replicate exactly that behaviour but a comma separated list can be easily > > implemented, eg) "clearcpuid=154,227" > > > > Make the clearcpuid parse a comma-separated list of values instead of only > > a single value. > > So I think the feature is broken as is; because it doesn't clear the > CPUID bits for userspace.
Usually it's enough to make the kernel stop using something. I used it many times for this.
People who want to affect user space usually run VMs anyways.
-Andi
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