This is a note to let you know that I've just added the patch titled

KVM: X86: Fix softlockup when get the current kvmclock

to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: kvm-x86-fix-softlockup-when-get-the-current-kvmclock.patch and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Thu Feb 1 13:45:42 CET 2018

From: Wanpeng Li kernellwp@gmail.com Date: Mon, 20 Nov 2017 14:55:05 -0800 Subject: KVM: X86: Fix softlockup when get the current kvmclock

From: Wanpeng Li kernellwp@gmail.com

[ Upstream commit e70b57a6ce4e8b92a56a615ae79bdb2bd66035e7 ]

watchdog: BUG: soft lockup - CPU#6 stuck for 22s! [qemu-system-x86:10185] CPU: 6 PID: 10185 Comm: qemu-system-x86 Tainted: G OE 4.14.0-rc4+ #4 RIP: 0010:kvm_get_time_scale+0x4e/0xa0 [kvm] Call Trace: get_time_ref_counter+0x5a/0x80 [kvm] kvm_hv_process_stimers+0x120/0x5f0 [kvm] kvm_arch_vcpu_ioctl_run+0x4b4/0x1690 [kvm] kvm_vcpu_ioctl+0x33a/0x620 [kvm] do_vfs_ioctl+0xa1/0x5d0 SyS_ioctl+0x79/0x90 entry_SYSCALL_64_fastpath+0x1e/0xa9

This can be reproduced when running kvm-unit-tests/hyperv_stimer.flat and cpu-hotplug stress simultaneously. __this_cpu_read(cpu_tsc_khz) returns 0 (set in kvmclock_cpu_down_prep()) when the pCPU is unhotplug which results in kvm_get_time_scale() gets into an infinite loop.

This patch fixes it by treating the unhotplug pCPU as not using master clock.

Reviewed-by: Radim Krčmář rkrcmar@redhat.com Reviewed-by: David Hildenbrand david@redhat.com Cc: Paolo Bonzini pbonzini@redhat.com Cc: Radim Krčmář rkrcmar@redhat.com Signed-off-by: Wanpeng Li wanpeng.li@hotmail.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Sasha Levin alexander.levin@verizon.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kvm/x86.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)

--- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1795,10 +1795,13 @@ u64 get_kvmclock_ns(struct kvm *kvm) /* both __this_cpu_read() and rdtsc() should be on the same cpu */ get_cpu();

- kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL, - &hv_clock.tsc_shift, - &hv_clock.tsc_to_system_mul); - ret = __pvclock_read_cycles(&hv_clock, rdtsc()); + if (__this_cpu_read(cpu_tsc_khz)) { + kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL, + &hv_clock.tsc_shift, + &hv_clock.tsc_to_system_mul); + ret = __pvclock_read_cycles(&hv_clock, rdtsc()); + } else + ret = ktime_get_boot_ns() + ka->kvmclock_offset;

put_cpu();

Patches currently in stable-queue which might be from kernellwp@gmail.com are

queue-4.14/kvm-x86-fix-softlockup-when-get-the-current-kvmclock.patch