Messages in this thread | | | Date | Tue, 8 Nov 2016 21:06:31 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH v10 6/7] x86/arch_prctl: Add ARCH_[GET|SET]_CPUID |
| |
On Tue, 8 Nov 2016, Kyle Huey wrote: > Intel supports faulting on the CPUID instruction beginning with Ivy Bridge. > When enabled, the processor will fault on attempts to execute the CPUID > instruction with CPL>0. Exposing this feature to userspace will allow a > ptracer to trap and emulate the CPUID instruction. > > When supported, this feature is controlled by toggling bit 0 of > MSR_MISC_FEATURES_ENABLES. It is documented in detail in Section 2.3.2 of > http://www.intel.com/content/dam/www/public/us/en/documents/application-notes/virtualization-technology-flexmigration-application-note.pdf
See previous mail.
> +DECLARE_PER_CPU(u64, msr_misc_features_enables_shadow); > + > diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c > index 97a340d..7d364e4 100644 > --- a/arch/x86/kernel/cpu/scattered.c > +++ b/arch/x86/kernel/cpu/scattered.c > @@ -71,9 +71,14 @@ void init_scattered_cpuid_features(struct cpuinfo_x86 *c) > } > > for (mb = msr_bits; mb->feature; mb++) { > if (rdmsrl_safe(mb->msr, &msrval)) > continue; > if (msrval & (1ULL << mb->bit)) > set_cpu_cap(c, mb->feature); > } > + > + if (cpu_has(c, X86_FEATURE_CPUID_FAULT)) { > + rdmsrl(MSR_MISC_FEATURES_ENABLES, msrval); > + this_cpu_write(msr_misc_features_enables_shadow, msrval); > + }
I'm not really happy about this placement. There is more stuff coming up which affects that MSR, so we should have a central place to handle it.
The most obvious is here:
> +DEFINE_PER_CPU(u64, msr_misc_features_enables_shadow);
void msr_misc_features_enable_init(struct cpuinfo_x86 *c) { u64 val;
if (rdmsrl_safe(MSR_MISC_FEATURES_ENABLES, val)) return;
this_cpu_write(msr_misc_features_enables_shadow, val); }
The upcoming ring3 mwait stuff can add its magic to tweak that MSR into this function.
Stick the call at the end of init_scattered_cpuid_features() for now. I still need to figure out a proper place for it.
> +static int set_cpuid_mode(struct task_struct *task, unsigned long val) > +{ > + /* Only disable_cpuid() if it is supported on this hardware. */
That comment makes no sense.
> + if (!static_cpu_has(X86_FEATURE_CPUID_FAULT)) > + return -ENODEV;
Thanks,
tglx
| |