linux-kernel - Re: [PATCH v1 1/5] KVM: arm/arm64: Remove kvm_mmio

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Message-ID: <5885c607-1314-ff53-38f1-9f48b1c16de4@huawei.com>
Date:   Thu, 13 Jun 2019 19:20:19 +0800
From:   Zenghui Yu <yuzenghui@...wei.com>
To:     James Morse <james.morse@....com>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <kvmarm@...ts.cs.columbia.edu>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-perf-users@...r.kernel.org>,
        <marc.zyngier@....com>, <catalin.marinas@....com>,
        <will.deacon@....com>, <acme@...nel.org>, <linuxarm@...wei.com>,
        <acme@...hat.com>, <peterz@...radead.org>,
        <alexander.shishkin@...ux.intel.com>, <mingo@...hat.com>,
        <ganapatrao.kulkarni@...ium.com>, <namhyung@...nel.org>,
        <jolsa@...hat.com>, <xiexiangyou@...wei.com>,
        "Wanghaibin (D)" <wanghaibin.wang@...wei.com>
Subject: Re: [PATCH v1 1/5] KVM: arm/arm64: Remove kvm_mmio_emulate tracepoint

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


.