Re: [PATCH] KVM: x86: fix lapic.timer_mode on restore

From: Paolo Bonzini <pbonzini@redhat.com>
To: "Radim Krčmář" <rkrcmar@redhat.com>, linux-kernel@vger.kernel.org
Cc: kvm@vger.kernel.org, stable@vger.kernel.org,
	Marcelo Tosatti <mtosatti@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] KVM: x86: fix lapic.timer_mode on restore
Date: Fri, 05 Jun 2015 21:08:32 +0200	[thread overview]
Message-ID: <5571F3B0.9060004@redhat.com> (raw)
In-Reply-To: <1433530661-31670-1-git-send-email-rkrcmar@redhat.com>

On 05/06/2015 20:57, Radim Krčmář wrote:
> lapic.timer_mode was not properly initialized after migration, which
> broke few useful things, like login, by making every sleep eternal.
> 
> Fix this by calling apic_update_lvtt in kvm_apic_post_state_restore.
> 
> There are other slowpaths that update lvtt, so this patch makes sure
> something similar doesn't happen again by calling apic_update_lvtt
> after every modification.
> 
> Cc: stable@vger.kernel.org
> Fixes: f30ebc312ca9 ("KVM: x86: optimize some accesses to LVTT and SPIV")
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
> ---
>  arch/x86/kvm/lapic.c | 26 ++++++++++++++++----------
>  1 file changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index beeef05bb4d9..36e9de1b4127 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1103,6 +1103,17 @@ static void update_divide_count(struct kvm_lapic *apic)
>  				   apic->divide_count);
>  }
>  
> +static void apic_update_lvtt(struct kvm_lapic *apic)
> +{
> +	u32 timer_mode = kvm_apic_get_reg(apic, APIC_LVTT) &
> +			apic->lapic_timer.timer_mode_mask;
> +
> +	if (apic->lapic_timer.timer_mode != timer_mode) {
> +		apic->lapic_timer.timer_mode = timer_mode;
> +		hrtimer_cancel(&apic->lapic_timer.timer);
> +	}
> +}
> +
>  static void apic_timer_expired(struct kvm_lapic *apic)
>  {
>  	struct kvm_vcpu *vcpu = apic->vcpu;
> @@ -1311,6 +1322,7 @@ static int apic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
>  				apic_set_reg(apic, APIC_LVTT + 0x10 * i,
>  					     lvt_val | APIC_LVT_MASKED);
>  			}
> +			apic_update_lvtt(apic);
>  			atomic_set(&apic->lapic_timer.pending, 0);
>  
>  		}
> @@ -1343,20 +1355,13 @@ static int apic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
>  
>  		break;
>  
> -	case APIC_LVTT: {
> -		u32 timer_mode = val & apic->lapic_timer.timer_mode_mask;
> -
> -		if (apic->lapic_timer.timer_mode != timer_mode) {
> -			apic->lapic_timer.timer_mode = timer_mode;
> -			hrtimer_cancel(&apic->lapic_timer.timer);
> -		}
> -
> +	case APIC_LVTT:
>  		if (!kvm_apic_sw_enabled(apic))
>  			val |= APIC_LVT_MASKED;
>  		val &= (apic_lvt_mask[0] | apic->lapic_timer.timer_mode_mask);
>  		apic_set_reg(apic, APIC_LVTT, val);
> +		apic_update_lvtt(apic);
>  		break;
> -	}
>  
>  	case APIC_TMICT:
>  		if (apic_lvtt_tscdeadline(apic))
> @@ -1588,7 +1593,7 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event)
>  
>  	for (i = 0; i < APIC_LVT_NUM; i++)
>  		apic_set_reg(apic, APIC_LVTT + 0x10 * i, APIC_LVT_MASKED);
> -	apic->lapic_timer.timer_mode = 0;
> +	apic_update_lvtt(apic);
>  	if (!(vcpu->kvm->arch.disabled_quirks & KVM_QUIRK_LINT0_REENABLED))
>  		apic_set_reg(apic, APIC_LVT0,
>  			     SET_APIC_DELIVERY_MODE(0, APIC_MODE_EXTINT));
> @@ -1816,6 +1821,7 @@ void kvm_apic_post_state_restore(struct kvm_vcpu *vcpu,
>  
>  	apic_update_ppr(apic);
>  	hrtimer_cancel(&apic->lapic_timer.timer);
> +	apic_update_lvtt(apic);
>  	update_divide_count(apic);
>  	start_apic_timer(apic);
>  	apic->irr_pending = true;
> 

Marcelo, if you have some free cycles feel free to apply this to
kvm/master and send it to Linus sometime next week.  I cannot do it on
Monday and I'll be on vacation afterwards.  (I'll be back as soon as
June 16th so I didn't plan on a formal handoff, but I think it's better
to have this in 4.1. The merge window conflicts with Linus's own
vacation and might be delayed).

And thanks Radim for the fix, it looks good.

Paolo