Re: [PATCH v3 10/16] KVM: x86: Drop current_vcpu for kvm_running_vcpu + kvm_arch_vcpu variable

Paolo Bonzini
2021-09-22T06:40:58Z

On 22/09/21 02:05, Sean Christopherson wrote:
> Use the generic kvm_running_vcpu plus a new 'handling_intr_from_guest'
> variable in kvm_arch_vcpu instead of the semi-redundant current_vcpu.
> kvm_before/after_interrupt() must be called while the vCPU is loaded,
> (which protects against preemption), thus kvm_running_vcpu is guaranteed
> to be non-NULL when handling_intr_from_guest is non-zero.
>
> Switching to kvm_get_running_vcpu() will allows moving KVM's perf
> callbacks to generic code, and the new flag will be used in a future
> patch to more precisely identify the "NMI from guest" case.
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/include/asm/kvm_host.h | 3 +--
> arch/x86/kvm/pmu.c | 2 +-
> arch/x86/kvm/x86.c | 21 ++++++++++++---------
> arch/x86/kvm/x86.h | 10 ++++++----
> 4 files changed, 20 insertions(+), 16 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 1080166fc0cf..2d86a2dfc775 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -763,6 +763,7 @@ struct kvm_vcpu_arch {
> unsigned nmi_pending; /* NMI queued after currently running handler */
> bool nmi_injected; /* Trying to inject an NMI this entry */
> bool smi_pending; /* SMI queued after currently running handler */
> + u8 handling_intr_from_guest;
>
> struct kvm_mtrr mtrr_state;
> u64 pat;
> @@ -1874,8 +1875,6 @@ int kvm_skip_emulated_instruction(struct kvm_vcpu *vcpu);
> int kvm_complete_insn_gp(struct kvm_vcpu *vcpu, int err);
> void __kvm_request_immediate_exit(struct kvm_vcpu *vcpu);
>
> -unsigned int kvm_guest_state(void);
> -
> void __user *__x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa,
> u32 size);
> bool kvm_vcpu_is_reset_bsp(struct kvm_vcpu *vcpu);
> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> index 5b68d4188de0..eef48258e50f 100644
> --- a/arch/x86/kvm/pmu.c
> +++ b/arch/x86/kvm/pmu.c
> @@ -87,7 +87,7 @@ static void kvm_perf_overflow_intr(struct perf_event *perf_event,
> * woken up. So we should wake it, but this is impossible from
> * NMI context. Do it from irq work instead.
> */
> - if (!kvm_guest_state())
> + if (!kvm_handling_nmi_from_guest(pmc->vcpu))
> irq_work_queue(&pmc_to_pmu(pmc)->irq_work);
> else
> kvm_make_request(KVM_REQ_PMI, pmc->vcpu);
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 6cc66466f301..24a6faa07442 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8264,15 +8264,17 @@ static void kvm_timer_init(void)
> kvmclock_cpu_online, kvmclock_cpu_down_prep);
> }
>
> -DEFINE_PER_CPU(struct kvm_vcpu *, current_vcpu);
> -EXPORT_PER_CPU_SYMBOL_GPL(current_vcpu);
> +static inline bool kvm_pmi_in_guest(struct kvm_vcpu *vcpu)
> +{
> + return vcpu && vcpu->arch.handling_intr_from_guest;
> +}
>
> -unsigned int kvm_guest_state(void)
> +static unsigned int kvm_guest_state(void)
> {
> - struct kvm_vcpu *vcpu = __this_cpu_read(current_vcpu);
> + struct kvm_vcpu *vcpu = kvm_get_running_vcpu();
> unsigned int state;
>
> - if (!vcpu)
> + if (!kvm_pmi_in_guest(vcpu))
> return 0;
>
> state = PERF_GUEST_ACTIVE;
> @@ -8284,9 +8286,10 @@ unsigned int kvm_guest_state(void)
>
> static unsigned long kvm_guest_get_ip(void)
> {
> - struct kvm_vcpu *vcpu = __this_cpu_read(current_vcpu);
> + struct kvm_vcpu *vcpu = kvm_get_running_vcpu();
>
> - if (WARN_ON_ONCE(!vcpu))
> + /* Retrieving the IP must be guarded by a call to kvm_guest_state(). */
> + if (WARN_ON_ONCE(!kvm_pmi_in_guest(vcpu)))
> return 0;
>
> return kvm_rip_read(vcpu);
> @@ -8294,10 +8297,10 @@ static unsigned long kvm_guest_get_ip(void)
>
> static unsigned int kvm_handle_intel_pt_intr(void)
> {
> - struct kvm_vcpu *vcpu = __this_cpu_read(current_vcpu);
> + struct kvm_vcpu *vcpu = kvm_get_running_vcpu();
>
> /* '0' on failure so that the !PT case can use a RET0 static call. */
> - if (!vcpu)
> + if (!kvm_pmi_in_guest(vcpu))
> return 0;
>
> kvm_make_request(KVM_REQ_PMI, vcpu);
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index 7d66d63dc55a..a9c107e7c907 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -387,18 +387,20 @@ static inline bool kvm_cstate_in_guest(struct kvm *kvm)
> return kvm->arch.cstate_in_guest;
> }
>
> -DECLARE_PER_CPU(struct kvm_vcpu *, current_vcpu);
> -
> static inline void kvm_before_interrupt(struct kvm_vcpu *vcpu)
> {
> - __this_cpu_write(current_vcpu, vcpu);
> + WRITE_ONCE(vcpu->arch.handling_intr_from_guest, 1);
> }
>
> static inline void kvm_after_interrupt(struct kvm_vcpu *vcpu)
> {
> - __this_cpu_write(current_vcpu, NULL);
> + WRITE_ONCE(vcpu->arch.handling_intr_from_guest, 0);
> }
>
> +static inline bool kvm_handling_nmi_from_guest(struct kvm_vcpu *vcpu)
> +{
> + return !!vcpu->arch.handling_intr_from_guest;
> +}
>
> static inline bool kvm_pat_valid(u64 data)
> {
>

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>