[Bug 59521] KVM linux guest reads uninitialized pvclock values before executing rdmsr MSR_KVM_WALL_CLOCK

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https://bugzilla.kernel.org/show_bug.cgi?id=59521





--- Comment #1 from Eugene Batalov <eabatalov89@gmail.com>  2013-06-11 16:03:55 ---
I have reconstructed the uninitialized pvclock read backtrace.
References to file lines are for Ubuntu-raring kernel
git://kernel.ubuntu.com/ubuntu/ubuntu-raring.git
tag is Ubuntu-3.8.0-19.30

bp: 0xf3ccbe68 ip: 0xc103cfbd
arch/x86/include/asm/pvclock.h:78
arch/x86/kernel/pvclock.c:74
bp: 0xf3ccbe70 ip: 0xc103c057
arch/x86/kernel/kvmclock.c:91
bp: 0xf3ccbe78 ip: 0xc1017598
arch/x86/kernel/tsc.c:58
bp: 0xf3ccbea8 ip: 0xc107e98d
kernel/sched/clock.c:248
bp: 0xf3ccbeb8 ip: 0xc107ea35
kernel/sched/clock.c:342
bp: 0xf3ccbf08 ip: 0xc104ad85
kernel/printk.c:356
bp: 0xf3ccbf50 ip: 0xc104c4e1
kernel/printk.c:1607
bp: 0xf3ccbf70 ip: 0xc1609bb6
kernel/printk.c:1688
bp: 0xf3ccbf90 ip: 0xc1600a51
arch/x86/include/asm/bitops.h:321
arch/x86/kernel/cpu/common.c:1325
bp: 0xf3ccbfb4 ip: 0xc1604000
??
bp: 0x00000000


kernel/printk.c:356
calls local_clock()
calls sched_clock_cpu()
calls sched_clock()
calls paravirt_sched_clock()
calls indirectly kvm_clock_read()
unintialized pv_clock is read here

vcpu kvmclock initialization is performed in kvm_register_clock.
kvm_register_clock is called from
static void __init kvm_smp_prepare_boot_cpu(void)
called form
 ./init/main.c:524 as smp_prepare_boot_cpu

I'll think about proper fix soon. We probably should fix cpu initialization
stages order or disable usage of pvclock before it initialized.

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