Nikolas Wipper <nikwip@xxxxxxxxx> writes:
> Introduce a suspension state for Hyper-V enlightened vCPUs. Microsoft's
> "Hypervisor Top Level Functional Specification" (TLFS) introduces this
> state as a "vCPU that is stopped on a instruction guest boundary, either
> explicitly or implicitly due to an intercept". The only documented
> explicit suspension is caused in response to a TLB Flush hypercall, which
> will use the state switching API in subsequent patches.
>
> Each Hyper-V vCPU now has a 'suspended' boolean field, which is checked
> before entering the guest. When set, it forces the vCPU to block. Once in
> that state, the vCPU ignores any events. The vCPU is unsuspended by
> clearing 'suspend' and issuing a request to force the vCPU out of sleep.
>
> Suspensions are issued as a mechanism to halt execution until state change
> is observed on a remote vCPU. Hyper-V vCPUs track this with 'waiting_on',
> which holds the 'vcpu_id' of the remote vCPU that forced the vCPU to enter
> the suspended state. It's the remote vCPU's responsibility to wake up the
> suspended vCPUs when ready. 'waiting_on' ensures the remote vCPU can
> selectively unsuspend vCPUs that blocked on its behalf while leaving other
> suspended vCPUs undisturbed. One vCPU can only be suspended due to a
> single remote vCPU, but different vCPUs can be suspended on behalf of
> different or the same remote vCPU(s). The guest is responsible for
> avoiding circular dependencies between suspended vCPUs.
>
> Callers of the suspend API are responsible for ensuring that suspend and
> unsuspend aren't called in parallel while targeting the same pair of
> vCPUs. Otherwise kvm_hv_vcpu_{un}suspend_tlb_flush() ensure 'waiting_on'
> and 'suspended' are updated and accessed in the correct order. This, for
> example, avoids races where the unsuspended vCPU re-suspends before
> kvm_hv_vcpu_unsuspend_tlb_flush() is done updating 'waiting_on'.
>
> Signed-off-by: Nikolas Wipper <nikwip@xxxxxxxxx>
> ---
> arch/x86/include/asm/kvm_host.h | 3 +++
> arch/x86/kvm/hyperv.c | 30 ++++++++++++++++++++++++++++++
> arch/x86/kvm/hyperv.h | 17 +++++++++++++++++
> arch/x86/kvm/x86.c | 4 +++-
> 4 files changed, 53 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 46e0a466d7fb..7571ac578884 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -695,6 +695,9 @@ struct kvm_vcpu_hv {
> u64 vm_id;
> u32 vp_id;
> } nested;
> +
> + bool suspended;
> + int waiting_on;
I don't quite understand why we need 'suspended' at all. Isn't it always
suspended when 'waiting_on != -1'? I can see we always update these two
in pair.
Also, I would suggest we use a more descriptive
name. 'waiting_on_vcpu_id', for example.
> };
>
> struct kvm_hypervisor_cpuid {
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index 4f0a94346d00..6e7941ed25ae 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -971,6 +971,7 @@ int kvm_hv_vcpu_init(struct kvm_vcpu *vcpu)
>
> vcpu->arch.hyperv = hv_vcpu;
> hv_vcpu->vcpu = vcpu;
> + hv_vcpu->waiting_on = -1;
>
> synic_init(&hv_vcpu->synic);
>
> @@ -2915,3 +2916,32 @@ int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
>
> return 0;
> }
> +
> +void kvm_hv_vcpu_suspend_tlb_flush(struct kvm_vcpu *vcpu, int vcpu_id)
Can we make parameter's name 'waiting_on_vcpu_id' as well? Because as-is
I'm getting confused which CPU of these two is actually getting
suspended)
Also, why do we need '_tlb_flush' in the name? The mechanism seems to be
fairly generic, it's just that we use it for TLB flushes.
> +{
> + /* waiting_on's store should happen before suspended's */
> + WRITE_ONCE(vcpu->arch.hyperv->waiting_on, vcpu_id);
> + WRITE_ONCE(vcpu->arch.hyperv->suspended, true);
> +}
> +
> +void kvm_hv_vcpu_unsuspend_tlb_flush(struct kvm_vcpu *vcpu)
And here someone may expect this means 'unsuspend vcpu' but in reality
this means 'unsuspend all vCPUs which are waiting on 'vcpu'). I guess we
need a rename. How about
void kvm_hv_unsuspend_vcpus(struct kvm_vcpu *waiting_on_vcpu)
?
> +{
> + DECLARE_BITMAP(vcpu_mask, KVM_MAX_VCPUS);
> + struct kvm_vcpu_hv *vcpu_hv;
> + struct kvm_vcpu *v;
> + unsigned long i;
> +
> + kvm_for_each_vcpu(i, v, vcpu->kvm) {
> + vcpu_hv = to_hv_vcpu(v);
> +
> + if (kvm_hv_vcpu_suspended(v) &&
> + READ_ONCE(vcpu_hv->waiting_on) == vcpu->vcpu_id) {
> + /* waiting_on's store should happen before suspended's */
> + WRITE_ONCE(v->arch.hyperv->waiting_on, -1);
> + WRITE_ONCE(v->arch.hyperv->suspended, false);
> + __set_bit(i, vcpu_mask);
> + }
> + }
> +
> + kvm_make_vcpus_request_mask(vcpu->kvm, KVM_REQ_EVENT, vcpu_mask);
> +}
> diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
> index 913bfc96959c..a55832cea221 100644
> --- a/arch/x86/kvm/hyperv.h
> +++ b/arch/x86/kvm/hyperv.h
> @@ -265,6 +265,15 @@ static inline void kvm_hv_nested_transtion_tlb_flush(struct kvm_vcpu *vcpu,
> }
>
> int kvm_hv_vcpu_flush_tlb(struct kvm_vcpu *vcpu);
> +
> +static inline bool kvm_hv_vcpu_suspended(struct kvm_vcpu *vcpu)
> +{
> + return vcpu->arch.hyperv_enabled &&
> + READ_ONCE(vcpu->arch.hyperv->suspended);
I don't think READ_ONCE() means anything here, does it?
> +}
> +
> +void kvm_hv_vcpu_suspend_tlb_flush(struct kvm_vcpu *vcpu, int vcpu_id);
> +void kvm_hv_vcpu_unsuspend_tlb_flush(struct kvm_vcpu *vcpu);
> #else /* CONFIG_KVM_HYPERV */
> static inline void kvm_hv_setup_tsc_page(struct kvm *kvm,
> struct pvclock_vcpu_time_info *hv_clock) {}
> @@ -321,6 +330,14 @@ static inline u32 kvm_hv_get_vpindex(struct kvm_vcpu *vcpu)
> return vcpu->vcpu_idx;
> }
> static inline void kvm_hv_nested_transtion_tlb_flush(struct kvm_vcpu *vcpu, bool tdp_enabled) {}
> +
> +static inline bool kvm_hv_vcpu_suspended(struct kvm_vcpu *vcpu)
> +{
> + return false;
> +}
> +
> +static inline void kvm_hv_vcpu_suspend_tlb_flush(struct kvm_vcpu *vcpu, int vcpu_id) {}
> +static inline void kvm_hv_vcpu_unsuspend_tlb_flush(struct kvm_vcpu *vcpu) {}
> #endif /* CONFIG_KVM_HYPERV */
>
> #endif /* __ARCH_X86_KVM_HYPERV_H__ */
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 15080385b8fe..18d0a300e79a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -135,6 +135,8 @@ static void store_regs(struct kvm_vcpu *vcpu);
> static int sync_regs(struct kvm_vcpu *vcpu);
> static int kvm_vcpu_do_singlestep(struct kvm_vcpu *vcpu);
>
> +static inline bool kvm_hv_vcpu_suspended(struct kvm_vcpu *vcpu);
> +
> static int __set_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2);
> static void __get_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2);
>
> @@ -11107,7 +11109,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> static bool kvm_vcpu_running(struct kvm_vcpu *vcpu)
> {
> return (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
> - !vcpu->arch.apf.halted);
> + !vcpu->arch.apf.halted && !kvm_hv_vcpu_suspended(vcpu));
> }
>
> static bool kvm_vcpu_has_events(struct kvm_vcpu *vcpu)
--
Vitaly
