linux-kernel - Re: [PATCH] kvm: disable stealtime via reboot notifier to avoid mem corruption

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Date:	Mon, 13 Aug 2012 18:52:31 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Florian Westphal <fw@...len.de>
Cc:	kvm@...r.kernel.org, avi@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kvm: disable stealtime via reboot notifier to avoid mem
 corruption

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@...len.de>
> ---
>  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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