Re: [PATCH v2] KVM: x86: Convert INIT and SIPI signals into synchronously handled requests

[Jan Kiszka <jan.kiszka@web.de>]

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On 2013-03-04 22:41, Jan Kiszka wrote:
> From: Jan Kiszka <jan.kiszka@siemens.com>
> 
> A VCPU sending INIT or SIPI to some other VCPU races for setting the
> remote VCPU's mp_state. When we were unlucky, KVM_MP_STATE_INIT_RECEIVED
> was overwritten by kvm_emulate_halt and, thus, got lost.
> 
> Fix this by raising requests on the sender side that will then be
> handled synchronously over the target VCPU context.
> 
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
> 
> Changes in v2:
>  - check transition to INIT_RECEIVED in vcpu_enter_guest
>  - removed return value of kvm_check_init_and_sipi - caller has to
>    check for relevant transition afterward
>  - add write barrier after setting sipi_vector
> 
>  arch/x86/kvm/lapic.c     |   11 ++++++-----
>  arch/x86/kvm/x86.c       |   15 +++++++++++++++
>  include/linux/kvm_host.h |    2 ++
>  3 files changed, 23 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 02b51dd..7986c9f 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -731,8 +731,7 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode,
>  	case APIC_DM_INIT:
>  		if (!trig_mode || level) {
>  			result = 1;
> -			vcpu->arch.mp_state = KVM_MP_STATE_INIT_RECEIVED;
> -			kvm_make_request(KVM_REQ_EVENT, vcpu);
> +			kvm_make_request(KVM_REQ_INIT, vcpu);
>  			kvm_vcpu_kick(vcpu);
>  		} else {
>  			apic_debug("Ignoring de-assert INIT to vcpu %d\n",
> @@ -743,11 +742,13 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode,
>  	case APIC_DM_STARTUP:
>  		apic_debug("SIPI to vcpu %d vector 0x%02x\n",
>  			   vcpu->vcpu_id, vector);
> -		if (vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) {
> +		if (vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED ||
> +		    test_bit(KVM_REQ_INIT, &vcpu->requests)) {
>  			result = 1;
>  			vcpu->arch.sipi_vector = vector;
> -			vcpu->arch.mp_state = KVM_MP_STATE_SIPI_RECEIVED;
> -			kvm_make_request(KVM_REQ_EVENT, vcpu);
> +			/* make sure sipi_vector is visible for the receiver */
> +			smp_wmb();
> +			kvm_make_request(KVM_REQ_SIPI, vcpu);
>  			kvm_vcpu_kick(vcpu);
>  		}
>  		break;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index d0cf737..0be04b9 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5641,6 +5641,15 @@ static void update_eoi_exitmap(struct kvm_vcpu *vcpu)
>  	kvm_x86_ops->load_eoi_exitmap(vcpu, eoi_exit_bitmap);
>  }
>  
> +static void kvm_check_init_and_sipi(struct kvm_vcpu *vcpu)
> +{
> +	if (kvm_check_request(KVM_REQ_INIT, vcpu))
> +		vcpu->arch.mp_state = KVM_MP_STATE_INIT_RECEIVED;

And here is a small race between clearing REQ_INIT and setting
INIT_RECEIVED. It can make the LAPIC drop the SIPI incorrectly. Need to
break up test and clear, doing the clear after mp_state update. Yeah...

Jan

> +	if (kvm_check_request(KVM_REQ_SIPI, vcpu) &&
> +	    vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED)
> +		vcpu->arch.mp_state = KVM_MP_STATE_SIPI_RECEIVED;
> +}
> +
>  static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  {
>  	int r;
> @@ -5649,6 +5658,11 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  	bool req_immediate_exit = 0;
>  
>  	if (vcpu->requests) {
> +		kvm_check_init_and_sipi(vcpu);
> +		if (vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) {
> +			r = 1;
> +			goto out;
> +		}
>  		if (kvm_check_request(KVM_REQ_MMU_RELOAD, vcpu))
>  			kvm_mmu_unload(vcpu);
>  		if (kvm_check_request(KVM_REQ_MIGRATE_TIMER, vcpu))
> @@ -6977,6 +6991,7 @@ void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
>  
>  int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
>  {
> +	kvm_check_init_and_sipi(vcpu);
>  	return (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
>  		!vcpu->arch.apf.halted)
>  		|| !list_empty_careful(&vcpu->async_pf.done)
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 722cae7..1a191c9 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -124,6 +124,8 @@ static inline bool is_error_page(struct page *page)
>  #define KVM_REQ_MCLOCK_INPROGRESS 20
>  #define KVM_REQ_EPR_EXIT          21
>  #define KVM_REQ_EOIBITMAP         22
> +#define KVM_REQ_INIT              23
> +#define KVM_REQ_SIPI              24
>  
>  #define KVM_USERSPACE_IRQ_SOURCE_ID		0
>  #define KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID	1
> 



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