hyperv-fixes for 5.11-rc5
x86/hyperv: Initialize clockevents after LAPIC is initialized
With commit 4df4cb9e99f8, the Hyper-V direct-mode STIMER is actually
initialized before LAPIC is initialized: see
setup_local_APIC() temporarily disables LAPIC, initializes it and
re-eanble it. The direct-mode STIMER depends on LAPIC, and when it's
registered, it can be programmed immediately and the timer can fire
When the timer fires in the hypervisor, if the LAPIC is in the
disabled state, new versions of Hyper-V ignore the event and don't inject
the timer interrupt into the VM, and hence the VM hangs when it boots.
Note: when the VM starts/reboots, the LAPIC is pre-enabled by the
firmware, so the window of LAPIC being temporarily disabled is pretty
small, and the issue can only happen once out of 100~200 reboots for
a 40-vCPU VM on one dev host, and on another host the issue doesn't
reproduce after 2000 reboots.
The issue is more noticeable for kdump/kexec, because the LAPIC is
disabled by the first kernel, and stays disabled until the kdump/kexec
kernel enables it. This is especially an issue to a Generation-2 VM
(for which Hyper-V doesn't emulate the PIT timer) when CONFIG_HZ=1000
(rather than CONFIG_HZ=250) is used.
Fix the issue by moving hv_stimer_alloc() to a later place where the
LAPIC timer is initialized.
Fixes: 4df4cb9e99f8 ("x86/hyperv: Initialize clockevents earlier in CPU onlining")
Signed-off-by: Dexuan Cui <firstname.lastname@example.org>
Reviewed-by: Michael Kelley <email@example.com>
Signed-off-by: Wei Liu <firstname.lastname@example.org>
1 file changed