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

Paolo Bonzini
2013-03-04T14:28:47Z

Il 03/03/2013 21:21, Jan Kiszka ha scritto:
> 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>
> ---
>
> Turned out to be simpler than expected. I'm no longer able to reproduce
> the race I saw before.
>
> arch/x86/kvm/lapic.c | 9 ++++-----
> arch/x86/kvm/x86.c | 16 +++++++++++++++-
> include/linux/kvm_host.h | 2 ++
> 3 files changed, 21 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 02b51dd..be1e37a 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 +742,11 @@ 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);
> + 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..8c8843c 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5641,6 +5641,18 @@ static void update_eoi_exitmap(struct kvm_vcpu *vcpu)
> kvm_x86_ops->load_eoi_exitmap(vcpu, eoi_exit_bitmap);
> }
>
> +static bool 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;
> + 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;

Do you need KVM_MP_STATE_SIPI_RECEIVED at all anymore? Perhaps you can
call kvm_check_init_and_sipi from __vcpu_run, before the call to
kvm_vcpu_block (and move the reset from __vcpu_run to
kvm_check_init_and_sipi too)? Then you do not even need to touch
kvm_arch_vcpu_runnable.

> + return true;
> + }
> + return false;
> +}
> +
> static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> {
> int r;
> @@ -5649,6 +5661,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> bool req_immediate_exit = 0;
>
> if (vcpu->requests) {
> + kvm_check_init_and_sipi(vcpu);

Does this need to return 1 if kvm_check_init_and_sipi returns 1?
Otherwise the guest is entered in INIT state. I think.

Paolo

> if (kvm_check_request(KVM_REQ_MMU_RELOAD, vcpu))
> kvm_mmu_unload(vcpu);
> if (kvm_check_request(KVM_REQ_MIGRATE_TIMER, vcpu))
> @@ -6977,10 +6990,11 @@ void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
>
> int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
> {
> + if (kvm_check_init_and_sipi(vcpu))
> + return 1;
> return (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
> !vcpu->arch.apf.halted)
> || !list_empty_careful(&vcpu->async_pf.done)
> - || vcpu->arch.mp_state == KVM_MP_STATE_SIPI_RECEIVED
> || atomic_read(&vcpu->arch.nmi_queued) ||
> (kvm_arch_interrupt_allowed(vcpu) &&
> kvm_cpu_has_interrupt(vcpu));
> 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
>