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Subject: Re: [PATCH v2] KVM: x86: Add tracepoint for dr_write/dr_read
From:   Haiwei Li <lihaiwei.kernel@gmail.com>
To:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc:     pbonzini@redhat.com, sean.j.christopherson@intel.com,
        vkuznets@redhat.com, wanpengli@tencent.com, jmattson@google.com,
        joro@8bytes.org, Haiwei Li <lihaiwei@tencent.com>
References: <20201009032130.6774-1-lihaiwei.kernel@gmail.com>
Message-ID: <eb80c1e1-152c-0bad-562d-ff07ed9685ea@gmail.com>
Date:   Fri, 6 Nov 2020 08:31:54 +0800
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Kindly ping. :)

On 20/10/9 11:21, lihaiwei.kernel@gmail.com wrote:
> From: Haiwei Li <lihaiwei@tencent.com>
> 
> When vmexit occurs caused by accessing dr, there is no tracepoint to track
> this action. Add tracepoint for this on x86 kvm.
> 
> Signed-off-by: Haiwei Li <lihaiwei@tencent.com>
> ---
> v1 -> v2:
>   * Improve the changelog
> 
>   arch/x86/kvm/svm/svm.c |  2 ++
>   arch/x86/kvm/trace.h   | 27 +++++++++++++++++++++++++++
>   arch/x86/kvm/vmx/vmx.c | 10 ++++++++--
>   arch/x86/kvm/x86.c     |  1 +
>   4 files changed, 38 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 4f401fc6a05d..52c69551aea4 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -2423,12 +2423,14 @@ static int dr_interception(struct vcpu_svm *svm)
>   		if (!kvm_require_dr(&svm->vcpu, dr - 16))
>   			return 1;
>   		val = kvm_register_read(&svm->vcpu, reg);
> +		trace_kvm_dr_write(dr - 16, val);
>   		kvm_set_dr(&svm->vcpu, dr - 16, val);
>   	} else {
>   		if (!kvm_require_dr(&svm->vcpu, dr))
>   			return 1;
>   		kvm_get_dr(&svm->vcpu, dr, &val);
>   		kvm_register_write(&svm->vcpu, reg, val);
> +		trace_kvm_dr_read(dr, val);
>   	}
>   
>   	return kvm_skip_emulated_instruction(&svm->vcpu);
> diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
> index aef960f90f26..b3bf54405862 100644
> --- a/arch/x86/kvm/trace.h
> +++ b/arch/x86/kvm/trace.h
> @@ -405,6 +405,33 @@ TRACE_EVENT(kvm_cr,
>   #define trace_kvm_cr_read(cr, val)		trace_kvm_cr(0, cr, val)
>   #define trace_kvm_cr_write(cr, val)		trace_kvm_cr(1, cr, val)
>   
> +/*
> + * Tracepoint for guest DR access.
> + */
> +TRACE_EVENT(kvm_dr,
> +	TP_PROTO(unsigned int rw, unsigned int dr, unsigned long val),
> +	TP_ARGS(rw, dr, val),
> +
> +	TP_STRUCT__entry(
> +		__field(	unsigned int,	rw		)
> +		__field(	unsigned int,	dr		)
> +		__field(	unsigned long,	val		)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->rw		= rw;
> +		__entry->dr		= dr;
> +		__entry->val		= val;
> +	),
> +
> +	TP_printk("dr_%s %x = 0x%lx",
> +		  __entry->rw ? "write" : "read",
> +		  __entry->dr, __entry->val)
> +);
> +
> +#define trace_kvm_dr_read(dr, val)		trace_kvm_dr(0, dr, val)
> +#define trace_kvm_dr_write(dr, val)		trace_kvm_dr(1, dr, val)
> +
>   TRACE_EVENT(kvm_pic_set_irq,
>   	    TP_PROTO(__u8 chip, __u8 pin, __u8 elcr, __u8 imr, bool coalesced),
>   	    TP_ARGS(chip, pin, elcr, imr, coalesced),
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 4551a7e80ebc..f78fd297d51e 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -5091,10 +5091,16 @@ static int handle_dr(struct kvm_vcpu *vcpu)
>   
>   		if (kvm_get_dr(vcpu, dr, &val))
>   			return 1;
> +		trace_kvm_dr_read(dr, val);
>   		kvm_register_write(vcpu, reg, val);
> -	} else
> -		if (kvm_set_dr(vcpu, dr, kvm_register_readl(vcpu, reg)))
> +	} else {
> +		unsigned long val;
> +
> +		val = kvm_register_readl(vcpu, reg);
> +		trace_kvm_dr_write(dr, val);
> +		if (kvm_set_dr(vcpu, dr, val))
>   			return 1;
> +	}
>   
>   	return kvm_skip_emulated_instruction(vcpu);
>   }
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c4015a43cc8a..68cb7b331324 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -11153,6 +11153,7 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_inj_virq);
>   EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_page_fault);
>   EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_msr);
>   EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_cr);
> +EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_dr);
>   EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_nested_vmrun);
>   EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_nested_vmexit);
>   EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_nested_vmexit_inject);
>