linux-kernel - Re: [PATCH v3 6/9] kvm: arm/arm64: Add host pmu to support VM introspection

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Message-ID: <87k29sms9h.fsf@e105922-lin.cambridge.arm.com>
Date:   Wed, 18 Jan 2017 13:06:50 +0000
From:   Punit Agrawal <punit.agrawal@....com>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        kvm@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v3 6/9] kvm: arm/arm64: Add host pmu to support VM introspection

Hi Marc,

Marc Zyngier <marc.zyngier@....com> writes:

> +Mark
>
> On 10/01/17 11:38, Punit Agrawal wrote:
>> Both AArch32 and AArch64 mode of the ARMv8 architecture support trapping
>> certain VM operations, e.g, TLB and cache maintenance
>> operations. Selective trapping of these operations for specific VMs can
>> be used to track the frequency with which these occur during execution.
>> 
>> Add a software PMU on the host that can support tracking VM
>> operations (in the form of PMU events). Supporting new events requires
>> providing callbacks to configure the VM to enable/disable the trapping
>> and read a count of the frequency.
>> 
>> The host PMU events can be controlled by tools like perf that use
>> standard kernel perf interfaces.
>> 
>> Signed-off-by: Punit Agrawal <punit.agrawal@....com>
>> Cc: Christoffer Dall <christoffer.dall@...aro.org>
>> Cc: Marc Zyngier <marc.zyngier@....com>
>> Cc: Will Deacon <will.deacon@....com>
>> ---
>>  arch/arm/include/asm/kvm_host.h   |   8 ++
>>  arch/arm/kvm/arm.c                |   2 +
>>  arch/arm64/include/asm/kvm_host.h |   8 ++
>>  virt/kvm/arm/host_pmu.c           | 272 ++++++++++++++++++++++++++++++++++++++
>>  4 files changed, 290 insertions(+)
>>  create mode 100644 virt/kvm/arm/host_pmu.c
>> 

[...]

>> 
>
> This patch really makes me think that there is nothing arm-specific in
> here at all. Why can't it be a generic feature through which
> architectures can expose events in a generic way (or as close as
> possible to being generic)?

I wasn't sure if other architectures are interested in the functionality
- that's the only reason. Having said that, it can be turned off in the
config so there shouldn't be any complaints.

I'll move this to virt/kvm in the next incarnation.

Thanks for taking a look.

>
> Thanks,
>
> 	M.