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Subject: Re: [PATCH v1 1/5] KVM: arm/arm64: Remove kvm_mmio_emulate tracepoint
To:     James Morse <james.morse@arm.com>
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References: <1560330526-15468-1-git-send-email-yuzenghui@huawei.com>
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From:   Zenghui Yu <yuzenghui@huawei.com>
Message-ID: <5885c607-1314-ff53-38f1-9f48b1c16de4@huawei.com>
Date:   Thu, 13 Jun 2019 19:20:19 +0800
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Hi James,

On 2019/6/12 20:48, James Morse wrote:
> Hi,
> 
> On 12/06/2019 10:08, Zenghui Yu wrote:
>> In current KVM/ARM code, no one will invoke trace_kvm_mmio_emulate().
>> Remove this TRACE_EVENT definition.
> 
> Oooer. We can't just go removing these things, they are visible to user-space.
> 
> I recall an article on this: https://lwn.net/Articles/737530/
> "Another attempt to address the tracepoint ABI problem"
> 
> I agree this is orphaned, it was added by commit 45e96ea6b369 ("KVM: ARM: Handle I/O
> aborts"), but there never was a caller.
> 
> The problem with removing it is /sys/kernel/debug/tracing/events/kvm/kvm_mmio_emulate
> disappears. Any program relying on that being present (but useless) is now broken.
Thanks for the reminder.

It turned out that I knew little about the tracepoint ABI :( .
I'm OK to just drop this patch in next version.


Thanks,
zenghui


.