On Thu, Sep 17, 2015 at 8:17 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > On Thu, Sep 17, 2015 at 08:17:18AM -0700, Andy Lutomirski wrote: > >> > Ah, that would be good news. Andy earlier argued I could not rely on >> > rdmsr_safe() faulting on unknown MSRs. If practically we can there's >> > some code I can simplify :-) >> >> I was taking about QEMU TCG, not KVM. > > Just for my education, TCG is the thing without _any_ hardware assist? Yes. > The thing you fear to use because it cannot boot a kernel this side of > tomorrow etc.. ? I actually use it on a semi-regular basis. It appears to boot a normal kernel correctly and surprisingly quickly. It's important for a silly reason. Asking KVM on an Intel host to emulate an AMD CPU or vice versa results in a chimera: I get an Opteron that's "GenuineIntel", which causes Linux to treat it as Intel, which means it gets the Intel quirks (SYSENTER in long mode, no X86_BUG_SYSRET_SS_ATTRS, etc) instead of the AMD quirks (SYSCALL in compat mode, etc). So, if I want to test compat SYSCALL, I have to use TCG, which will actually do a decent job of emulating an AMD CPU for me. Maybe Paolo can fix QEMU to fail bad MSR accesses for real... --Andy -- Andy Lutomirski AMA Capital Management, LLC -- 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
