x86: kvmclock: zero initialize pvclock shared memory area

commit 07868fc6aaf57847b0f3a3d53086b7556eb83f4a upstream.

kernel might hung in pvclock_clocksource_read() due to
uninitialized memory might contain odd version value in
following cycle:

        do {
                version = __pvclock_read_cycles(src, &ret, &flags);
        } while ((src->version & 1) || version != src->version);

if secondary kvmclock is accessed before it's registered with kvm.

Clear garbage in pvclock shared memory area right after it's
allocated to avoid this issue.

Ref: https://bugzilla.kernel.org/show_bug.cgi?id=59521
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
[See BZ for analysis.  We may want a different fix for 3.11, but
 this is the safest for now - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index 0732f0089a3df2d0bcbde6b397fc8c3e1e76844c..1590a3a88b7748043a82796e8e5fdc5d07903361 100644 (file)
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -238,6 +238,7 @@ void __init kvmclock_init(void)
        if (!mem)
                return;
        hv_clock = __va(mem);
+       memset(hv_clock, 0, size);
 
        if (kvm_register_clock("boot clock")) {
                hv_clock = NULL;