linux-kernel - Re: [PATCH v2] KVM: arm/arm64: Introduce kvm_pmu_vcpu

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Date:   Tue, 23 Jul 2019 09:26:04 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Julien Thierry <julien.thierry@....com>
Cc:     Zenghui Yu <yuzenghui@...wei.com>, <kvmarm@...ts.cs.columbia.edu>,
        <linux-arm-kernel@...ts.infradead.org>, <james.morse@....com>,
        <suzuki.poulose@....com>, <julien.thierry.kdev@...il.com>,
        <linux-kernel@...r.kernel.org>, <wanghaibin.wang@...wei.com>,
        <andrew.murray@....com>
Subject: Re: [PATCH v2] KVM: arm/arm64: Introduce kvm_pmu_vcpu_init() to setup PMU counter idx

On 2019-07-23 09:17, Julien Thierry wrote:
> Hi Zenghui,
>
> On 18/07/2019 09:15, Zenghui Yu wrote:
>> We use "pmc->idx" and the "chained" bitmap to determine if the pmc 
>> is
>> chained, in kvm_pmu_pmc_is_chained().  But idx might be 
>> uninitialized
>> (and random) when we doing this decision, through a 
>> KVM_ARM_VCPU_INIT
>> ioctl -> kvm_pmu_vcpu_reset(). And the test_bit() against this 
>> random
>> idx will potentially hit a KASAN BUG [1].
>>
>> In general, idx is the static property of a PMU counter that is not
>> expected to be modified across resets, as suggested by Julien.  It
>> looks more reasonable if we can setup the PMU counter idx for a vcpu
>> in its creation time. Introduce a new function - kvm_pmu_vcpu_init()
>> for this basic setup. Oh, and the KASAN BUG will get fixed this way.
>>
>> [1] https://www.spinics.net/lists/kvm-arm/msg36700.html
>>
>> Fixes: 80f393a23be6 ("KVM: arm/arm64: Support chained PMU counters")
>> Suggested-by: Andrew Murray <andrew.murray@....com>
>> Suggested-by: Julien Thierry <julien.thierry@....com>
>> Cc: Marc Zyngier <maz@...nel.org>
>> Signed-off-by: Zenghui Yu <yuzenghui@...wei.com>
>> ---
>>
>> Changes since v1:
>>  - Introduce kvm_pmu_vcpu_init() in vcpu's creation time, move the
>>    assignment of pmc->idx into it.
>>  - Thus change the subject. The old one is "KVM: arm/arm64: Assign
>>    pmc->idx before kvm_pmu_stop_counter()".
>>
>> Julien, I haven't collected your Acked-by into this version. If 
>> you're
>> still happy with the change, please Ack again. Thanks!
>>
>
> Thanks for making the change. This looks good to me:
>
> Acked-by: Julien Thierry <julien.thierry@....com>

Applied, thanks both.

         M.
-- 
Jazz is not dead. It just smells funny...