linux-kernel - Re: [PATCH v2 3/3] KVM: x86: correct async page present tracepoint

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Date:   Tue, 21 Mar 2017 09:57:07 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH v2 3/3] KVM: x86: correct async page present tracepoint

On 21.03.2017 05:18, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@...mail.com>
> 
> After async pf setup successfully, there is a broadcast wakeup w/ special 
> token 0xffffffff which tells vCPU that it should wake up all processes 
> waiting for APFs though there is no real process waiting at the moment.
> 
> The async page present tracepoint print prematurely and fails to catch the 
> special token setup. This patch fixes it by moving the async page present 
> tracepoint after the special token setup.
> 
> Before patch:
> 
> qemu-system-x86-8499  [006] ...1  5973.473292: kvm_async_pf_ready: token 0x0 gva 0x0
> 
> After patch:
> 
> qemu-system-x86-8499  [006] ...1  5973.473292: kvm_async_pf_ready: token 0xffffffff gva 0x0
> 

Wonder if there is a reason why this is traced before any work is done.
Maybe we should keep that order (by breaking up the if-else).

> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
> ---
>  arch/x86/kvm/x86.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 1faf620..e27eb7f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8566,11 +8566,11 @@ void kvm_arch_async_page_present(struct kvm_vcpu *vcpu,
>  {
>  	struct x86_exception fault;
>  
> -	trace_kvm_async_pf_ready(work->arch.token, work->gva);
>  	if (work->wakeup_all)
>  		work->arch.token = ~0; /* broadcast wakeup */
>  	else
>  		kvm_del_async_pf_gfn(vcpu, work->arch.gfn);
> +	trace_kvm_async_pf_ready(work->arch.token, work->gva);
>  
>  	if ((vcpu->arch.apf.msr_val & KVM_ASYNC_PF_ENABLED) &&
>  	    !apf_put_user(vcpu, KVM_PV_REASON_PAGE_READY)) {
> 


-- 

Thanks,

David