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Date: Mon, 21 Sep 2015 21:40:19 -0300 From: Marcelo Tosatti <mtosatti@...hat.com> To: Radim Krčmář <rkrcmar@...hat.com> Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>, Luiz Capitulino <lcapitulino@...hat.com> Subject: Re: [RFC PATCH 0/2] kvmclock: fix ABI breakage from PVCLOCK_COUNTS_FROM_ZERO. > So either: > > Proceed with guest solution: > -> Make sure the overflow can't happen (and write down why not in the > code). Don't assume a small delta between kvmclock values of vcpus. > -> Handle stable -> non-stable kvmclock transition. > -> kvmclock counts from zero should not depend on stable kvmclock > (because nohz_full should work on hpet host systems). > > Enable counts-from-zero on MSR_KVM_SYSTEM_TIME_NEW: > -> Figure out whats wrong with different kvmclock values on hotplug, > and fix it. Find data which allows you to differentiate between hotplug of pCPU-0 and system initialization. Easy one: whether MSR_KVM_SYSTEM_TIME_NEW contains valid data (that is kvmclock is enabled) for vCPUs other than vCPU-0. This can't be the case on system initialization (otherwise the host will be corrupting guest memory), and must be the case when hotplugging vCPU-0. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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