linux-kernel - Re: [PATCH v3 10/16] KVM: x86: Drop current_vcpu for kvm_running_vcpu + kvm_arch

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Date:   Wed, 22 Sep 2021 08:40:47 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Marc Zyngier <maz@...nel.org>, Guo Ren <guoren@...nel.org>,
        Nick Hu <nickhu@...estech.com>,
        Greentime Hu <green.hu@...il.com>,
        Vincent Chen <deanbo422@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>
Cc:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Stefano Stabellini <sstabellini@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, linux-csky@...r.kernel.org,
        linux-riscv@...ts.infradead.org, kvm@...r.kernel.org,
        xen-devel@...ts.xenproject.org,
        Artem Kashkanov <artem.kashkanov@...el.com>,
        Like Xu <like.xu.linux@...il.com>,
        Zhu Lingshan <lingshan.zhu@...el.com>
Subject: Re: [PATCH v3 10/16] KVM: x86: Drop current_vcpu for kvm_running_vcpu
 + kvm_arch_vcpu variable

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@...gle.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@...hat.com>