Re: [PATCH] kvm: disable stealtime via reboot notifier to avoid memcorruption

From: Marcelo Tosatti
Date: Mon Aug 13 2012 - 18:09:22 EST


On Fri, Aug 10, 2012 at 12:36:22PM +0200, Florian Westphal wrote:
> else, we get memory corruption on reboot; found when tracking down
> initramfs unpack error on initial reboot (with qemu-kvm -smp 2,
> no problem with single-core).
>
> problem with doing it via kvm_shutdown() is that this file
> depends on CONFIG_KVM_CLOCK, also its not enough to call it for one
> cpu only.
>
> Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
> ---
> not subscribed, please CC on replies.
> Also, I don't know much about kvm or kexec, so its possible
> that i missed something.
>
> In any case, this seems to fix the initramfs corruption for me.
> patch is against virt/kvm/kvm.git.
>
> arch/x86/kernel/kvm.c | 1 +
> arch/x86/kernel/kvmclock.c | 1 -
> 2 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index c1d61ee..1596cc8 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -354,6 +354,7 @@ static void kvm_pv_guest_cpu_reboot(void *unused)
> if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
> wrmsrl(MSR_KVM_PV_EOI_EN, 0);
> kvm_pv_disable_apf();
> + kvm_disable_steal_time();
> }
>
> static int kvm_pv_reboot_notify(struct notifier_block *nb,

This part below will introduce a bug for shutdown. Can you retest with
the addition of kvm_disable_steal_time to kvm_pv_guest_cpu_reboot only,
retest and resend please?

Thanks

> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> index f1b42b3..5a2fa7d 100644
> --- a/arch/x86/kernel/kvmclock.c
> +++ b/arch/x86/kernel/kvmclock.c
> @@ -191,7 +191,6 @@ static void kvm_crash_shutdown(struct pt_regs *regs)
> static void kvm_shutdown(void)
> {
> native_write_msr(msr_kvm_system_time, 0, 0);
> - kvm_disable_steal_time();
> native_machine_shutdown();
> }
>
> --
> 1.7.8.6
>
> --
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