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

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Date:   Wed, 6 Dec 2017 16:11:50 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Neil Leeder <nleeder@...eaurora.org>
Cc:     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 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?

Thanks,
Mark.

> 
> 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.
>