https://bugzilla.kernel.org/show_bug.cgi?id=216177 --- Comment #9 from Yang Lixiao (lixiao.yang@xxxxxxxxx) --- (In reply to Jim Mattson from comment #8) > On Mon, Jun 27, 2022 at 8:54 PM Nadav Amit <nadav.amit@xxxxxxxxx> wrote: > > > The failure on bare-metal that I experienced hints that this is either a > test > > bug or (much less likely) a hardware bug. But I do not think it is likely > to > > be > > a KVM bug. > > KVM does not use the VMX-preemption timer to virtualize L1's > VMX-preemption timer (and that is why KVM is broken). The KVM bug was > introduced with commit f4124500c2c1 ("KVM: nVMX: Fully emulate > preemption timer"), which uses an L0 CLOCK_MONOTONIC hrtimer to > emulate L1's VMX-preemption timer. There are many reasons that this > cannot possibly work, not the least of which is that the > CLOCK_MONOTONIC timer is subject to time slew. > > Currently, KVM reserves L0's VMX-preemption timer for emulating L1's > APIC timer. Better would be to determine whether L1's APIC timer or > L1's VMX-preemption timer is scheduled to fire first, and use L0's > VMX-preemption timer to trigger a VM-exit on the nearest alarm. > Alternatively, as Sean noted, one could perhaps arrange for the > hrtimer to fire early enough that it won't fire late, but I don't > really think that's a viable solution. > > I can't explain the bare-metal failures, but I will note that the test > assumes the default treatment of SMIs and SMM. The test will likely > fail with the dual-monitor treatment of SMIs and SMM. Aside from the > older CPUs with broken VMX-preemption timers, I don't know of any > relevant errata. > > Of course, it is possible that the test itself is buggy. For the > person who reported bare-metal failures on Ice Lake and Cooper Lake, > how long was the test in VMX non-root mode past the VMX-preemption > timer deadline? On the first Ice lake: Test suite: vmx_preemption_timer_expiry_test FAIL: Last stored guest TSC (28067103426) < TSC deadline (28067086048) On the second Ice lake: Test suite: vmx_preemption_timer_expiry_test FAIL: Last stored guest TSC (27014488614) < TSC deadline (27014469152) On Cooper lake: Test suite: vmx_preemption_timer_expiry_test FAIL: Last stored guest TSC (29030585690) < TSC deadline (29030565024) -- You may reply to this email to add a comment. You are receiving this mail because: You are watching the assignee of the bug.
