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    Subject[RFC PATCH 2/5] KVM: arm64: Move WFI execution to check_vcpu_requests()
    Date
    Prepare for WFI requests from userspace, by adding a suspend request and
    moving the WFI execution into check_vcpu_requests(), next to the
    power-off logic.

    vcpu->arch.mp_state, previously only RUNNABLE or STOPPED, supports an
    additional state HALTED and two new state transitions:

    RUNNABLE -> HALTED from WFI or PSCI CPU_SUSPEND (same vCPU)
    HALTED -> RUNNABLE vGIC IRQ, pending timer, signal

    There shouldn't be any functional change with this patch, even though
    the KVM_GET_MP_STATE ioctl could now in theory return
    KVM_MP_STATE_HALTED, which would break some users' mp_state support. In
    practice it should not happen because we do not return to userspace with
    HALTED state. Both WFI and PSCI CPU_SUSPEND stay in the vCPU run loop
    until the suspend request is consumed. It does feel fragile though,
    maybe we should explicitly return RUNNABLE in KVM_GET_MP_STATE in place
    of HALTED, to prevent future breakage.

    Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
    ---
    arch/arm64/include/asm/kvm_host.h | 2 ++
    arch/arm64/kvm/arm.c | 18 ++++++++++++++-
    arch/arm64/kvm/handle_exit.c | 3 +--
    arch/arm64/kvm/psci.c | 37 +++++++++++++------------------
    4 files changed, 35 insertions(+), 25 deletions(-)

    diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
    index 55a04f4d5919..3ca732feb9a5 100644
    --- a/arch/arm64/include/asm/kvm_host.h
    +++ b/arch/arm64/include/asm/kvm_host.h
    @@ -46,6 +46,7 @@
    #define KVM_REQ_VCPU_RESET KVM_ARCH_REQ(2)
    #define KVM_REQ_RECORD_STEAL KVM_ARCH_REQ(3)
    #define KVM_REQ_RELOAD_GICv4 KVM_ARCH_REQ(4)
    +#define KVM_REQ_SUSPEND KVM_ARCH_REQ(5)

    #define KVM_DIRTY_LOG_MANUAL_CAPS (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE | \
    KVM_DIRTY_LOG_INITIALLY_SET)
    @@ -722,6 +723,7 @@ int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu,
    struct kvm_device_attr *attr);
    void kvm_arm_vcpu_power_off(struct kvm_vcpu *vcpu);
    bool kvm_arm_vcpu_is_off(struct kvm_vcpu *vcpu);
    +void kvm_arm_vcpu_suspend(struct kvm_vcpu *vcpu);

    /* Guest/host FPSIMD coordination helpers */
    int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu);
    diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
    index bcc24adb9c0a..d8cbaa0373c7 100644
    --- a/arch/arm64/kvm/arm.c
    +++ b/arch/arm64/kvm/arm.c
    @@ -447,6 +447,12 @@ bool kvm_arm_vcpu_is_off(struct kvm_vcpu *vcpu)
    return vcpu->arch.mp_state == KVM_MP_STATE_STOPPED;
    }

    +void kvm_arm_vcpu_suspend(struct kvm_vcpu *vcpu)
    +{
    + vcpu->arch.mp_state = KVM_MP_STATE_HALTED;
    + kvm_make_request(KVM_REQ_SUSPEND, vcpu);
    +}
    +
    int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu *vcpu,
    struct kvm_mp_state *mp_state)
    {
    @@ -667,6 +673,8 @@ static int kvm_vcpu_initialized(struct kvm_vcpu *vcpu)

    static void check_vcpu_requests(struct kvm_vcpu *vcpu)
    {
    + bool irq_pending;
    +
    if (kvm_request_pending(vcpu)) {
    if (kvm_check_request(KVM_REQ_SLEEP, vcpu))
    vcpu_req_sleep(vcpu);
    @@ -678,7 +686,7 @@ static void check_vcpu_requests(struct kvm_vcpu *vcpu)
    * Clear IRQ_PENDING requests that were made to guarantee
    * that a VCPU sees new virtual interrupts.
    */
    - kvm_check_request(KVM_REQ_IRQ_PENDING, vcpu);
    + irq_pending = kvm_check_request(KVM_REQ_IRQ_PENDING, vcpu);

    if (kvm_check_request(KVM_REQ_RECORD_STEAL, vcpu))
    kvm_update_stolen_time(vcpu);
    @@ -690,6 +698,14 @@ static void check_vcpu_requests(struct kvm_vcpu *vcpu)
    vgic_v4_load(vcpu);
    preempt_enable();
    }
    +
    + if (kvm_check_request(KVM_REQ_SUSPEND, vcpu)) {
    + if (!irq_pending) {
    + kvm_vcpu_block(vcpu);
    + kvm_clear_request(KVM_REQ_UNHALT, vcpu);
    + }
    + vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
    + }
    }
    }

    diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
    index 6f48336b1d86..9717df3104cf 100644
    --- a/arch/arm64/kvm/handle_exit.c
    +++ b/arch/arm64/kvm/handle_exit.c
    @@ -95,8 +95,7 @@ static int kvm_handle_wfx(struct kvm_vcpu *vcpu)
    } else {
    trace_kvm_wfx_arm64(*vcpu_pc(vcpu), false);
    vcpu->stat.wfi_exit_stat++;
    - kvm_vcpu_block(vcpu);
    - kvm_clear_request(KVM_REQ_UNHALT, vcpu);
    + kvm_arm_vcpu_suspend(vcpu);
    }

    kvm_incr_pc(vcpu);
    diff --git a/arch/arm64/kvm/psci.c b/arch/arm64/kvm/psci.c
    index 24b4a2265dbd..42a307ceb95f 100644
    --- a/arch/arm64/kvm/psci.c
    +++ b/arch/arm64/kvm/psci.c
    @@ -31,27 +31,6 @@ static unsigned long psci_affinity_mask(unsigned long affinity_level)
    return 0;
    }

    -static unsigned long kvm_psci_vcpu_suspend(struct kvm_vcpu *vcpu)
    -{
    - /*
    - * NOTE: For simplicity, we make VCPU suspend emulation to be
    - * same-as WFI (Wait-for-interrupt) emulation.
    - *
    - * This means for KVM the wakeup events are interrupts and
    - * this is consistent with intended use of StateID as described
    - * in section 5.4.1 of PSCI v0.2 specification (ARM DEN 0022A).
    - *
    - * Further, we also treat power-down request to be same as
    - * stand-by request as-per section 5.4.2 clause 3 of PSCI v0.2
    - * specification (ARM DEN 0022A). This means all suspend states
    - * for KVM will preserve the register state.
    - */
    - kvm_vcpu_block(vcpu);
    - kvm_clear_request(KVM_REQ_UNHALT, vcpu);
    -
    - return PSCI_RET_SUCCESS;
    -}
    -
    static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu *source_vcpu)
    {
    struct vcpu_reset_state *reset_state;
    @@ -227,7 +206,21 @@ static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu)
    break;
    case PSCI_0_2_FN_CPU_SUSPEND:
    case PSCI_0_2_FN64_CPU_SUSPEND:
    - val = kvm_psci_vcpu_suspend(vcpu);
    + /*
    + * NOTE: For simplicity, we make VCPU suspend emulation to be
    + * same-as WFI (Wait-for-interrupt) emulation.
    + *
    + * This means for KVM the wakeup events are interrupts and this
    + * is consistent with intended use of StateID as described in
    + * section 5.4.1 of PSCI v0.2 specification (ARM DEN 0022A).
    + *
    + * Further, we also treat power-down request to be same as
    + * stand-by request as-per section 5.4.2 clause 3 of PSCI v0.2
    + * specification (ARM DEN 0022A). This means all suspend states
    + * for KVM will preserve the register state.
    + */
    + kvm_arm_vcpu_suspend(vcpu);
    + val = PSCI_RET_SUCCESS;
    break;
    case PSCI_0_2_FN_CPU_OFF:
    kvm_arm_vcpu_power_off(vcpu);
    --
    2.31.1
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