On Thu, Feb 17, 2011, Avi Kivity wrote about "Re: Why exit on MSR_STAR and friends?": > It isn't needed. The code doesn't distinguish between the read and > write bitmaps, and so far no guest issues rdmsr for these msrs with any > frequency (kvm as a guest will write those msrs, but it shouldn't read > them on Intel). Do you see frequent reads on some guest? I saw reads of all these MSRs (STAR, LSTAR, CSTAR and SYSCALL_MASK) at about half the number of the writes. Looking deeper now, I realize why I saw these and you didn't. I happened to run some old L1 image, with apparently a 1 year old Linux and KVM. In that version, __vmx_load_host_state() called: save_msrs(vmx->guest_msrs, vmx->save_nmsrs); load_msrs(vmx->host_msrs, vmx->save_nmsrs); and save_msrs read all those MSRs. Looking at the current code, indeed this is no loger done. So you can say that there are some guests which frequently reads those MSRs - old versions of KVM :-) But I agree, this is nothing to worry about. I guess I should be more worried why I got all these PIOs in L2 in the first place - the MSR reads and writes in L1 were just an odd consequence of that. It turns out that the "ping -f" workload I was running in L2 insisted to get accurate timings of each packet, and this, I'm not still sure why, caused a ACPI PM_TIMER PIO for each packet. I guess that normal workloads won't use the timer on every packet, so that shouldn't matter. -- Nadav Har'El | Thursday, Feb 17 2011, 13 Adar I 5771 nyh@xxxxxxxxxxxxxxxxxxx |----------------------------------------- Phone +972-523-790466, ICQ 13349191 |Knowledge is knowing a tomato is a fruit. http://nadav.harel.org.il |Wisdom is not putting it in a fruit salad. -- 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