diff mbox

x86: kvmclock: zero initialize pvclock shared memory area

Message ID 1370881871-13130-1-git-send-email-imammedo@redhat.com (mailing list archive)
State New, archived
Headers show

Commit Message

Igor Mammedov June 10, 2013, 4:31 p.m. UTC

Comments

Marcelo Tosatti June 10, 2013, 8:19 p.m. UTC | #1 
On Mon, Jun 10, 2013 at 06:31:11PM +0200, Igor Mammedov wrote:
> ===
> Could be the following an acceptable fix?
> ===

Read of kvmclock should return proper value from hypervisor: system
timestamp + tsc delta.

Should find the offender site and have it register MSR_KVM_SYSTEM_TIME 
before reading the area.

> 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>
> ---
>  arch/x86/kernel/kvmclock.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> index d2c3812..3dd37eb 100644
> --- a/arch/x86/kernel/kvmclock.c
> +++ b/arch/x86/kernel/kvmclock.c
> @@ -242,6 +242,7 @@ 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;
> -- 
> 1.7.1
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diff mbox

Patch

===
Could be the following an acceptable fix?
===

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>
---
 arch/x86/kernel/kvmclock.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index d2c3812..3dd37eb 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -242,6 +242,7 @@  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;