Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754494Ab3FOSDG (ORCPT ); Sat, 15 Jun 2013 14:03:06 -0400 Received: from mx2.parallels.com ([199.115.105.18]:51672 "EHLO mx2.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754381Ab3FOSDE (ORCPT ); Sat, 15 Jun 2013 14:03:04 -0400 From: Eugene Batalov To: CC: Eugene Batalov , , , , Subject: [PATCHv1] kvm guest: fix uninitialized kvmclock read by KVM guest Date: Sat, 15 Jun 2013 22:01:45 +0400 Message-ID: <1371319305-590-1-git-send-email-ebatalov@parallels.com> X-Mailer: git-send-email 1.7.9.5 In-Reply-To: <20130610201933.GA31409@amt.cnet> References: <20130610201933.GA31409@amt.cnet> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2762 Lines: 78 Due to unintialized kvmclock read KVM guest is hanging on SMP boot stage. If unintialized memory contains fatal garbage then hang reproduction is 100%. Unintialized memory is allocated by memblock_alloc. So the garbage values depend on many many things. See the detailed description of the bug and possible ways to fix it in the kernel bug tracker. "Bug 59521 - KVM linux guest reads uninitialized pvclock values before executing rdmsr MSR_KVM_WALL_CLOCK" I decided to fix it simply returning 0ULL from kvm_clock_read when kvm clocksource is not initialized yet. The same as kernel bootstrap CPU doesn on boot stage when kernel clocksources are not initialized yet. Signed-off-by: Eugene Batalov --- I dont' use kernel percpu variables because for each SMP CPU their contents are copied from the bootstrap CPU. And I don't think that fixing the value for each SMP CPU is a good style. If you know a better approach to store the is_pv_clock_ready flags I am ready to use it. The patch applies cleanly to git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git I've tested the changes with Ubuntu 13.04 "raring" userspace and Ubuntu-3.8.0.19-30 kernel tag. arch/x86/kernel/kvmclock.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c index 5bedbdd..a6e0af4 100644 --- a/arch/x86/kernel/kvmclock.c +++ b/arch/x86/kernel/kvmclock.c @@ -43,6 +43,9 @@ early_param("no-kvmclock", parse_no_kvmclock); static struct pvclock_vsyscall_time_info *hv_clock; static struct pvclock_wall_clock wall_clock; +/* For each cpu store here a flag which tells whether pvclock is initialized */ +static int __cacheline_aligned_in_smp is_pv_clock_ready[NR_CPUS] = {}; + /* * The wallclock is the time of day when we booted. Since then, some time may * have elapsed since the hypervisor wrote the data. So we try to account for @@ -84,8 +87,11 @@ static cycle_t kvm_clock_read(void) preempt_disable_notrace(); cpu = smp_processor_id(); - src = &hv_clock[cpu].pvti; - ret = pvclock_clocksource_read(src); + if (is_pv_clock_ready[cpu]) { + src = &hv_clock[cpu].pvti; + ret = pvclock_clocksource_read(src); + } else + ret = 0ULL; preempt_enable_notrace(); return ret; } @@ -168,6 +174,9 @@ int kvm_register_clock(char *txt) printk(KERN_INFO "kvm-clock: cpu %d, msr %x:%x, %s\n", cpu, high, low, txt); + if (!ret) + is_pv_clock_ready[cpu] = 1; + return ret; } -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/