On 01/02/12 12:20, Peter Maydell wrote: > On 1 February 2012 12:11, Marc Zyngier <marc.zyngier@xxxxxxx> wrote: >> The obvious fix would be to test for the virt extensions in ID_PFR1 >> before enabling KVM, and mask out the virt extensions from the same >> register in the guest by trapping CP15-c0. But c0 is used by cache >> maintenance operations, and trapping would lead to unacceptable >> performance degradation. > > You can just set HCR.TID3 to get hyp traps on only the feature > ID registers, right? (traps access to only ID_PFR0, ID_PFR1, ID_DFR0, > ID_AFR0, ID_MMFR0, ID_MMFR1, ID_MMFR2, ID_MMFR3, ID_ISAR0, ID_ISAR1, > ID_ISAR2, ID_ISAR3, ID_ISAR4, ID_ISAR5, MVFR0, and MVFR1, none > of which should be on performance-critical paths I hope.) Good catch. It looks much better, except that ID_MMFR3 is used in cpu_v7_set_pte_ext(), which is called each time you map a page. Ouch. I'm not even sure we can the cache ID_MMFR3 in the kernel (multi-cluster systems may have different features). M. -- Jazz is not dead. It just smells funny... -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
