linux-kernel - Re: [PATCH v3 2/5] KVM: X86: Introduce need_cancel_enter

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Date:   Mon, 27 Apr 2020 11:30:13 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Haiwei Li <lihaiwei@...cent.com>
Subject: Re: [PATCH v3 2/5] KVM: X86: Introduce need_cancel_enter_guest helper

On Fri, Apr 24, 2020 at 02:22:41PM +0800, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@...cent.com>
> 
> Introduce need_cancel_enter_guest() helper, we need to check some 
> conditions before doing CONT_RUN, in addition, it can also catch 
> the case vmexit occurred while another event was being delivered 
> to guest software since vmx_complete_interrupts() adds the request 
> bit.
> 
> Tested-by: Haiwei Li <lihaiwei@...cent.com>
> Cc: Haiwei Li <lihaiwei@...cent.com>
> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 12 +++++++-----
>  arch/x86/kvm/x86.c     | 10 ++++++++--
>  arch/x86/kvm/x86.h     |  1 +
>  3 files changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index f1f6638..5c21027 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6577,7 +6577,7 @@ bool __vmx_vcpu_run(struct vcpu_vmx *vmx, unsigned long *regs, bool launched);
>  
>  static enum exit_fastpath_completion vmx_vcpu_run(struct kvm_vcpu *vcpu)
>  {
> -	enum exit_fastpath_completion exit_fastpath;
> +	enum exit_fastpath_completion exit_fastpath = EXIT_FASTPATH_NONE;
>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
>  	unsigned long cr3, cr4;
>  
> @@ -6754,10 +6754,12 @@ static enum exit_fastpath_completion vmx_vcpu_run(struct kvm_vcpu *vcpu)
>  	vmx_recover_nmi_blocking(vmx);
>  	vmx_complete_interrupts(vmx);
>  
> -	exit_fastpath = vmx_exit_handlers_fastpath(vcpu);
> -	/* static call is better with retpolines */
> -	if (exit_fastpath == EXIT_FASTPATH_CONT_RUN)
> -		goto cont_run;
> +	if (!kvm_need_cancel_enter_guest(vcpu)) {
> +		exit_fastpath = vmx_exit_handlers_fastpath(vcpu);
> +		/* static call is better with retpolines */
> +		if (exit_fastpath == EXIT_FASTPATH_CONT_RUN)
> +			goto cont_run;
> +	}
>  
>  	return exit_fastpath;
>  }
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 59958ce..4561104 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1581,6 +1581,13 @@ int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu)
>  }
>  EXPORT_SYMBOL_GPL(kvm_emulate_wrmsr);
>  
> +bool kvm_need_cancel_enter_guest(struct kvm_vcpu *vcpu)

What about kvm_vcpu_<???>_pending()?  Not sure what a good ??? would be.
The "cancel_enter_guest" wording is a bit confusing when this is called
from the VM-Exit path.

> +{
> +	return (vcpu->mode == EXITING_GUEST_MODE || kvm_request_pending(vcpu)
> +	    || need_resched() || signal_pending(current));

Parantheses around the whole statement are unnecessary.  Personal preference
is to put the || before the newline.

> +}
> +EXPORT_SYMBOL_GPL(kvm_need_cancel_enter_guest);
> +
>  /*
>   * The fast path for frequent and performance sensitive wrmsr emulation,
>   * i.e. the sending of IPI, sending IPI early in the VM-Exit flow reduces
> @@ -8373,8 +8380,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  	if (kvm_lapic_enabled(vcpu) && vcpu->arch.apicv_active)
>  		kvm_x86_ops.sync_pir_to_irr(vcpu);
>  
> -	if (vcpu->mode == EXITING_GUEST_MODE || kvm_request_pending(vcpu)
> -	    || need_resched() || signal_pending(current)) {
> +	if (kvm_need_cancel_enter_guest(vcpu)) {
>  		vcpu->mode = OUTSIDE_GUEST_MODE;
>  		smp_wmb();
>  		local_irq_enable();
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index 7b5ed8e..1906e7e 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -364,5 +364,6 @@ static inline bool kvm_dr7_valid(u64 data)
>  void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu);
>  void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu);
>  u64 kvm_spec_ctrl_valid_bits(struct kvm_vcpu *vcpu);
> +bool kvm_need_cancel_enter_guest(struct kvm_vcpu *vcpu);
>  
>  #endif
> -- 
> 2.7.4
>