On Thu, Jul 10, 2014 at 03:59:43AM -0700, kan.li...@intel.com wrote: > +/* > + * Under certain circumstances, access certain MSR may cause #GP. > + * The function tests if the input MSR can be safely accessed. > + */ > +static inline bool check_msr(unsigned long msr) > +{ > + u64 val_old, val_new, val_tmp; > + > + /* > + * Read the current value, change it and read it back to see if it > + * matches, this is needed to detect certain hardware emulators > + * (qemu/kvm) that don't trap on the MSR access and always return 0s. > + */ > + if (rdmsrl_safe(msr, &val_old)) > + goto msr_fail; > + /* > + * Only chagne it slightly, > + * since the higher bits of some MSRs cannot be updated by wrmsrl. > + * E.g. MSR_LBR_TOS > + */ > + val_tmp = val_old ^ 0x3UL; > + if (wrmsrl_safe(msr, val_tmp) || > + rdmsrl_safe(msr, &val_new)) > + goto msr_fail; > + > + if (val_new != val_tmp) > + goto msr_fail; > + > + /* Here it's sure that the MSR can be safely accessed. > + * Restore the old value and return. > + */ > + wrmsrl(msr, val_old); > + > + return true; > + > +msr_fail: > + return false; > +}
I don't think we need the msr_fail thing, there's no state to clean up, you can return false at all places you now have goto.
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