[PATCH v5 07/13] KVM: arm64: Add support for userspace to suspend a vCPU
Reiji Watanabe
reijiw at google.com
Wed Apr 20 20:12:31 PDT 2022
Hi Oliver,
On Sat, Apr 9, 2022 at 11:46 AM Oliver Upton <oupton at google.com> wrote:
>
> Introduce a new MP state, KVM_MP_STATE_SUSPENDED, which indicates a vCPU
> is in a suspended state. In the suspended state the vCPU will block
> until a wakeup event (pending interrupt) is recognized.
>
> Add a new system event type, KVM_SYSTEM_EVENT_WAKEUP, to indicate to
> userspace that KVM has recognized one such wakeup event. It is the
> responsibility of userspace to then make the vCPU runnable, or leave it
> suspended until the next wakeup event.
>
> Signed-off-by: Oliver Upton <oupton at google.com>
> ---
> Documentation/virt/kvm/api.rst | 37 +++++++++++++++++++++--
> arch/arm64/include/asm/kvm_host.h | 1 +
> arch/arm64/kvm/arm.c | 49 +++++++++++++++++++++++++++++++
> include/uapi/linux/kvm.h | 2 ++
> 4 files changed, 87 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index d13fa6600467..d104e34ad703 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -1476,14 +1476,43 @@ Possible values are:
> [s390]
> KVM_MP_STATE_LOAD the vcpu is in a special load/startup state
> [s390]
> + KVM_MP_STATE_SUSPENDED the vcpu is in a suspend state and is waiting
> + for a wakeup event [arm64]
> ========================== ===============================================
>
> On x86, this ioctl is only useful after KVM_CREATE_IRQCHIP. Without an
> in-kernel irqchip, the multiprocessing state must be maintained by userspace on
> these architectures.
>
> -For arm64/riscv:
> -^^^^^^^^^^^^^^^^
> +For arm64:
> +^^^^^^^^^^
> +
> +If a vCPU is in the KVM_MP_STATE_SUSPENDED state, KVM will emulate the
> +architectural execution of a WFI instruction.
> +
> +If a wakeup event is recognized, KVM will exit to userspace with a
> +KVM_SYSTEM_EVENT exit, where the event type is KVM_SYSTEM_EVENT_WAKEUP. If
> +userspace wants to honor the wakeup, it must set the vCPU's MP state to
> +KVM_MP_STATE_RUNNABLE. If it does not, KVM will continue to await a wakeup
> +event in subsequent calls to KVM_RUN.
> +
> +.. warning::
> +
> + If userspace intends to keep the vCPU in a SUSPENDED state, it is
> + strongly recommended that userspace take action to suppress the
> + wakeup event (such as masking an interrupt). Otherwise, subsequent
> + calls to KVM_RUN will immediately exit with a KVM_SYSTEM_EVENT_WAKEUP
> + event and inadvertently waste CPU cycles.
> +
> + Additionally, if userspace takes action to suppress a wakeup event,
> + it is strongly recommended that it also restores the vCPU to its
> + original state when the vCPU is made RUNNABLE again. For example,
> + if userspace masked a pending interrupt to suppress the wakeup,
> + the interrupt should be unmasked before returning control to the
> + guest.
> +
> +For riscv:
> +^^^^^^^^^^
>
> The only states that are valid are KVM_MP_STATE_STOPPED and
> KVM_MP_STATE_RUNNABLE which reflect if the vcpu is paused or not.
> @@ -5985,6 +6014,7 @@ should put the acknowledged interrupt vector into the 'epr' field.
> #define KVM_SYSTEM_EVENT_SHUTDOWN 1
> #define KVM_SYSTEM_EVENT_RESET 2
> #define KVM_SYSTEM_EVENT_CRASH 3
> + #define KVM_SYSTEM_EVENT_WAKEUP 4
> __u32 type;
> __u64 flags;
> } system_event;
> @@ -6009,6 +6039,9 @@ Valid values for 'type' are:
> has requested a crash condition maintenance. Userspace can choose
> to ignore the request, or to gather VM memory core dump and/or
> reset/shutdown of the VM.
> + - KVM_SYSTEM_EVENT_WAKEUP -- the exiting vCPU is in a suspended state and
> + KVM has recognized a wakeup event. Userspace may honor this event by
> + marking the exiting vCPU as runnable, or deny it and call KVM_RUN again.
>
> Valid flags are:
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index f3f93d48e21a..46027b9b80ca 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -46,6 +46,7 @@
> #define KVM_REQ_RECORD_STEAL KVM_ARCH_REQ(3)
> #define KVM_REQ_RELOAD_GICv4 KVM_ARCH_REQ(4)
> #define KVM_REQ_RELOAD_PMU KVM_ARCH_REQ(5)
> +#define KVM_REQ_SUSPEND KVM_ARCH_REQ(6)
>
> #define KVM_DIRTY_LOG_MANUAL_CAPS (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE | \
> KVM_DIRTY_LOG_INITIALLY_SET)
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index efe54aba5cce..e9641b86d375 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -444,6 +444,18 @@ bool kvm_arm_vcpu_stopped(struct kvm_vcpu *vcpu)
> return vcpu->arch.mp_state.mp_state == KVM_MP_STATE_STOPPED;
> }
>
> +static void kvm_arm_vcpu_suspend(struct kvm_vcpu *vcpu)
> +{
> + vcpu->arch.mp_state.mp_state = KVM_MP_STATE_SUSPENDED;
> + kvm_make_request(KVM_REQ_SUSPEND, vcpu);
> + kvm_vcpu_kick(vcpu);
> +static void kvm_arm_vcpu_suspend(struct kvm_vcpu *vcpu)
> +{
> + vcpu->arch.mp_state.mp_state = KVM_MP_STATE_SUSPENDED;
> + kvm_make_request(KVM_REQ_SUSPEND, vcpu);
> + kvm_vcpu_kick(vcpu);
Considering the patch 8 will remove the call to kvm_vcpu_kick()
(BTW, I wonder why you wanted to make that change in the patch-8
instead of the patch-7), it looks like we could use the mp_state
KVM_MP_STATE_SUSPENDED instead of using KVM_REQ_SUSPEND.
What is the reason why you prefer to introduce KVM_REQ_SUSPEND
rather than simply using KVM_MP_STATE_SUSPENDED ?
Thanks,
Reiji
> +}
> +
> +static bool kvm_arm_vcpu_suspended(struct kvm_vcpu *vcpu)
> +{
> + return vcpu->arch.mp_state.mp_state == KVM_MP_STATE_SUSPENDED;
> +}
> +
> int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu *vcpu,
> struct kvm_mp_state *mp_state)
> {
> @@ -464,6 +476,9 @@ int kvm_arch_vcpu_ioctl_set_mpstate(struct kvm_vcpu *vcpu,
> case KVM_MP_STATE_STOPPED:
> kvm_arm_vcpu_power_off(vcpu);
> break;
> + case KVM_MP_STATE_SUSPENDED:
> + kvm_arm_vcpu_suspend(vcpu);
> + break;
> default:
> ret = -EINVAL;
> }
> @@ -648,6 +663,37 @@ void kvm_vcpu_wfi(struct kvm_vcpu *vcpu)
> preempt_enable();
> }
>
> +static int kvm_vcpu_suspend(struct kvm_vcpu *vcpu)
> +{
> + if (!kvm_arm_vcpu_suspended(vcpu))
> + return 1;
> +
> + kvm_vcpu_wfi(vcpu);
> +
> + /*
> + * The suspend state is sticky; we do not leave it until userspace
> + * explicitly marks the vCPU as runnable. Request that we suspend again
> + * later.
> + */
> + kvm_make_request(KVM_REQ_SUSPEND, vcpu);
> +
> + /*
> + * Check to make sure the vCPU is actually runnable. If so, exit to
> + * userspace informing it of the wakeup condition.
> + */
> + if (kvm_arch_vcpu_runnable(vcpu)) {
> + kvm_vcpu_set_system_event_exit(vcpu, KVM_SYSTEM_EVENT_WAKEUP, 0);
> + return 0;
> + }
> +
> + /*
> + * Otherwise, we were unblocked to process a different event, such as a
> + * pending signal. Return 1 and allow kvm_arch_vcpu_ioctl_run() to
> + * process the event.
> + */
> + return 1;
> +}
> +
> /**
> * check_vcpu_requests - check and handle pending vCPU requests
> * @vcpu: the VCPU pointer
> @@ -686,6 +732,9 @@ static int check_vcpu_requests(struct kvm_vcpu *vcpu)
> if (kvm_check_request(KVM_REQ_RELOAD_PMU, vcpu))
> kvm_pmu_handle_pmcr(vcpu,
> __vcpu_sys_reg(vcpu, PMCR_EL0));
> +
> + if (kvm_check_request(KVM_REQ_SUSPEND, vcpu))
> + return kvm_vcpu_suspend(vcpu);
> }
>
> return 1;
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 91a6fe4e02c0..64e5f9d83a7a 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -444,6 +444,7 @@ struct kvm_run {
> #define KVM_SYSTEM_EVENT_SHUTDOWN 1
> #define KVM_SYSTEM_EVENT_RESET 2
> #define KVM_SYSTEM_EVENT_CRASH 3
> +#define KVM_SYSTEM_EVENT_WAKEUP 4
> __u32 type;
> __u64 flags;
> } system_event;
> @@ -640,6 +641,7 @@ struct kvm_vapic_addr {
> #define KVM_MP_STATE_OPERATING 7
> #define KVM_MP_STATE_LOAD 8
> #define KVM_MP_STATE_AP_RESET_HOLD 9
> +#define KVM_MP_STATE_SUSPENDED 10
>
> struct kvm_mp_state {
> __u32 mp_state;
> --
> 2.35.1.1178.g4f1659d476-goog
>
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