From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751598AbdKFAzc (ORCPT ); Sun, 5 Nov 2017 19:55:32 -0500 Received: from mail-pg0-f68.google.com ([74.125.83.68]:55791 "EHLO mail-pg0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751550AbdKFAza (ORCPT ); Sun, 5 Nov 2017 19:55:30 -0500 X-Google-Smtp-Source: ABhQp+Tx0KB/INQABXPlVs0AKXrvL1N5jVnmZGOW4m+1/IozHBTbjcWMkJz9DTaj3CNQDK6rCJkY9Q== From: Wanpeng Li X-Google-Original-From: Wanpeng Li To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Paolo Bonzini , =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= , Wanpeng Li Subject: [PATCH] KVM: X86: Fix softlockup when get the current kvmclock timestamp Date: Sun, 5 Nov 2017 16:55:21 -0800 Message-Id: <1509929721-3027-1-git-send-email-wanpeng.li@hotmail.com> X-Mailer: git-send-email 2.7.4 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Wanpeng Li 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_kvmclock_ns+0xa3/0x140 [kvm] get_time_ref_counter+0x5a/0x80 [kvm] kvm_hv_process_stimers+0x120/0x5f0 [kvm] ? kvm_hv_process_stimers+0x120/0x5f0 [kvm] ? preempt_schedule+0x27/0x30 ? ___preempt_schedule+0x16/0x18 kvm_arch_vcpu_ioctl_run+0x4b4/0x1690 [kvm] ? kvm_arch_vcpu_load+0x47/0x230 [kvm] kvm_vcpu_ioctl+0x33a/0x620 [kvm] ? kvm_vcpu_ioctl+0x33a/0x620 [kvm] ? kvm_vm_ioctl_check_extension_generic+0x3b/0x40 [kvm] ? kvm_dev_ioctl+0x279/0x6c0 [kvm] do_vfs_ioctl+0xa1/0x5d0 ? __fget+0x73/0xa0 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. kvm_get_time_scale() takes too long which results in softlockup. This patch fixes it by disabling preemption just for rdtsc() and __this_cpu_read() section in order to reduce preemption disable time, the per-CPU variable is just read operation and the master clock is active, so it is as safe as how it is used in kvm_guest_time_update(). Cc: Paolo Bonzini Cc: Radim Krčmář Signed-off-by: Wanpeng Li --- arch/x86/kvm/x86.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 34c85aa..2542f9b 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1781,6 +1781,7 @@ u64 get_kvmclock_ns(struct kvm *kvm) struct kvm_arch *ka = &kvm->arch; struct pvclock_vcpu_time_info hv_clock; u64 ret; + unsigned long this_tsc_khz, host_tsc; spin_lock(&ka->pvclock_gtod_sync_lock); if (!ka->use_master_clock) { @@ -1795,13 +1796,17 @@ 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()); + this_tsc_khz = __this_cpu_read(cpu_tsc_khz); + host_tsc = rdtsc(); put_cpu(); + /* With all the info we got, fill in the values */ + kvm_get_time_scale(NSEC_PER_SEC, this_tsc_khz * 1000LL, + &hv_clock.tsc_shift, + &hv_clock.tsc_to_system_mul); + ret = __pvclock_read_cycles(&hv_clock, host_tsc); + return ret; } -- 2.7.4