linux-kernel - Re: [PATCH] perf: qcom_l2_pmu: don't allow guest access

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Date:   Wed, 6 Dec 2017 16:19:24 -0500
From:   "Leeder, Neil" <nleeder@...eaurora.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     nleeder@...eaurora.org, Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Mark Langsdorf <mlangsdo@...hat.com>,
        Mark Salter <msalter@...hat.com>, Jon Masters <jcm@...hat.com>,
        Timur Tabi <timur@...eaurora.org>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH] perf: qcom_l2_pmu: don't allow guest access

On 12/6/2017 11:11 AM, Mark Rutland wrote:
> On Wed, Dec 06, 2017 at 10:55:33AM -0500, Neil Leeder wrote:
>> Guests cannot access IMPDEF system registers, which are used
>> by this driver. Disable the driver if it's running in a guest VM.
>>
>> Signed-off-by: Neil Leeder <nleeder@...eaurora.org>
>> ---
>>  drivers/perf/qcom_l2_pmu.c | 4 ++++
>>  1 file changed, 4 insertions(+)
> 
> Hi Neil,
> 
> I'm a little confused by this. Why is this hypervisor providing a
> QCOM8130 device to the guest that it cannot use?
> 
> Could you elaborate on what's going on?
> 
Hi Mark,

While there's an argument that the guest shouldn't be loading the driver
in the first place, we can't control everyone's guest configuration or what
their hypervisor does.

>>
>> diff --git a/drivers/perf/qcom_l2_pmu.c b/drivers/perf/qcom_l2_pmu.c
>> index 4fdc848..49dc954 100644
>> --- a/drivers/perf/qcom_l2_pmu.c
>> +++ b/drivers/perf/qcom_l2_pmu.c
>> @@ -1057,6 +1057,10 @@ static int __init register_l2_cache_pmu_driver(void)
>>  {
>>  	int err;
>>  
>> +	/* Don't enable driver if running as guest */
>> +	if (!is_hyp_mode_available())
>> +		return 0;
>> +
>>  	err = cpuhp_setup_state_multi(CPUHP_AP_PERF_ARM_QCOM_L2_ONLINE,
>>  				      "AP_PERF_ARM_QCOM_L2_ONLINE",
>>  				      l2cache_pmu_online_cpu,
>> -- 
>> Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies Inc.
>> Qualcomm Technologies, Inc. is a member of the Code Aurora Forum,
>> a Linux Foundation Collaborative Project.
>>

Neil
-- 
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.