linux-kernel - Re: [PATCH v3 7/9] context_tracking: KVM: Move guest enter/exit wrappers to KVM's domain

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Date:   Wed, 21 Apr 2021 09:10:22 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Michael Tokarev <mjt@....msk.ru>,
        Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [PATCH v3 7/9] context_tracking: KVM: Move guest enter/exit
 wrappers to KVM's domain



On 16.04.21 00:21, Sean Christopherson wrote:
> Move the guest enter/exit wrappers to kvm_host.h so that KVM can manage
> its context tracking vs. vtime accounting without bleeding too many KVM
> details into the context tracking code.
> 
> No functional change intended.

Funny story. This used to be in kvm code and it was moved to context_tracking by
commit 521921bad1192fb1b8f9b6a5aa673635848b8b5f
     kvm: Move guest entry/exit APIs to context_tracking

I think with all your cleanup it can now move back as it no longer deals with
context tracking.


> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>   include/linux/context_tracking.h | 45 --------------------------------
>   include/linux/kvm_host.h         | 45 ++++++++++++++++++++++++++++++++
>   2 files changed, 45 insertions(+), 45 deletions(-)
> 
> diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
> index e172a547b2d0..d4dc9c4d79aa 100644
> --- a/include/linux/context_tracking.h
> +++ b/include/linux/context_tracking.h
> @@ -118,49 +118,4 @@ extern void context_tracking_init(void);
>   static inline void context_tracking_init(void) { }
>   #endif /* CONFIG_CONTEXT_TRACKING_FORCE */
>   
> -/* must be called with irqs disabled */
> -static __always_inline void guest_enter_irqoff(void)
> -{
> -	/*
> -	 * This is running in ioctl context so its safe to assume that it's the
> -	 * stime pending cputime to flush.
> -	 */
> -	instrumentation_begin();
> -	vtime_account_guest_enter();
> -	instrumentation_end();
> -
> -	/*
> -	 * KVM does not hold any references to rcu protected data when it
> -	 * switches CPU into a guest mode. In fact switching to a guest mode
> -	 * is very similar to exiting to userspace from rcu point of view. In
> -	 * addition CPU may stay in a guest mode for quite a long time (up to
> -	 * one time slice). Lets treat guest mode as quiescent state, just like
> -	 * we do with user-mode execution.
> -	 */
> -	if (!context_tracking_guest_enter_irqoff()) {
> -		instrumentation_begin();
> -		rcu_virt_note_context_switch(smp_processor_id());
> -		instrumentation_end();
> -	}
> -}
> -
> -static __always_inline void guest_exit_irqoff(void)
> -{
> -	context_tracking_guest_exit_irqoff();
> -
> -	instrumentation_begin();
> -	/* Flush the guest cputime we spent on the guest */
> -	vtime_account_guest_exit();
> -	instrumentation_end();
> -}
> -
> -static inline void guest_exit(void)
> -{
> -	unsigned long flags;
> -
> -	local_irq_save(flags);
> -	guest_exit_irqoff();
> -	local_irq_restore(flags);
> -}
> -
>   #endif
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 3b06d12ec37e..444d5f0225cb 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -332,6 +332,51 @@ struct kvm_vcpu {
>   	struct kvm_dirty_ring dirty_ring;
>   };
>   
> +/* must be called with irqs disabled */
> +static __always_inline void guest_enter_irqoff(void)
> +{
> +	/*
> +	 * This is running in ioctl context so its safe to assume that it's the
> +	 * stime pending cputime to flush.
> +	 */
> +	instrumentation_begin();
> +	vtime_account_guest_enter();
> +	instrumentation_end();
> +
> +	/*
> +	 * KVM does not hold any references to rcu protected data when it
> +	 * switches CPU into a guest mode. In fact switching to a guest mode
> +	 * is very similar to exiting to userspace from rcu point of view. In
> +	 * addition CPU may stay in a guest mode for quite a long time (up to
> +	 * one time slice). Lets treat guest mode as quiescent state, just like
> +	 * we do with user-mode execution.
> +	 */
> +	if (!context_tracking_guest_enter_irqoff()) {
> +		instrumentation_begin();
> +		rcu_virt_note_context_switch(smp_processor_id());
> +		instrumentation_end();
> +	}
> +}
> +
> +static __always_inline void guest_exit_irqoff(void)
> +{
> +	context_tracking_guest_exit_irqoff();
> +
> +	instrumentation_begin();
> +	/* Flush the guest cputime we spent on the guest */
> +	vtime_account_guest_exit();
> +	instrumentation_end();
> +}
> +
> +static inline void guest_exit(void)
> +{
> +	unsigned long flags;
> +
> +	local_irq_save(flags);
> +	guest_exit_irqoff();
> +	local_irq_restore(flags);
> +}
> +
>   static inline int kvm_vcpu_exiting_guest_mode(struct kvm_vcpu *vcpu)
>   {
>   	/*
>