linux-kernel - Re: [PATCH 2/2] KVM: arm/arm64: Print the EC hex value with its exact width

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Message-ID: <e013e828-5e61-8c07-510f-6cb4c59367cf@huawei.com>
Date:   Wed, 11 Sep 2019 17:19:05 +0800
From:   Zenghui Yu <yuzenghui@...wei.com>
To:     Marc Zyngier <maz@...nel.org>
CC:     <james.morse@....com>, <julien.thierry.kdev@...il.com>,
        <suzuki.poulose@....com>, <kvmarm@...ts.cs.columbia.edu>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <wanghaibin.wang@...wei.com>
Subject: Re: [PATCH 2/2] KVM: arm/arm64: Print the EC hex value with its exact
 width

Hi Marc,

On 2019/9/11 16:31, Marc Zyngier wrote:
> On Wed, 11 Sep 2019 03:33:36 +0100,
> Zenghui Yu <yuzenghui@...wei.com> wrote:
>>
>> EC is the bits [31:26] of ESR_ELx on arm64 (HSR on arm). Print the
>> hex value with its exact width (8).
>>
>> Signed-off-by: Zenghui Yu <yuzenghui@...wei.com>
>> ---
>>   virt/kvm/arm/trace.h | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/virt/kvm/arm/trace.h b/virt/kvm/arm/trace.h
>> index 204d210d01c2..022b0a060034 100644
>> --- a/virt/kvm/arm/trace.h
>> +++ b/virt/kvm/arm/trace.h
>> @@ -42,7 +42,7 @@ TRACE_EVENT(kvm_exit,
>>   		__entry->vcpu_pc		= vcpu_pc;
>>   	),
>>   
>> -	TP_printk("%s: HSR_EC: 0x%04x (%s), PC: 0x%08lx",
>> +	TP_printk("%s: HSR_EC: 0x%02x (%s), PC: 0x%08lx",
>>   		  __print_symbolic(__entry->ret, kvm_arm_exception_type),
>>   		  __entry->esr_ec,
>>   		  __print_symbolic(__entry->esr_ec, kvm_arm_exception_class),
> 
> Although you're right that 8 bits ought to be enough, this is a change
> to the output of the tracepoint, which userspace could (does?) parse.

Well-written userspace tools should only parse the low 8 bits (if they
do parse). But even if the high bits are parsed, they're always 0.
So I don't think this change will have a bad impact on userspace.

> I'm thus reluctant to change anything there, knowing that we don't
> lose any information, and just print two extra zeroes.

Anyway this is not a fix, feel free to ignore it if you're worried about
that there might be some issues ;)

> Am I missing anything?

No.


Thanks,
zenghui