linux-kernel - Re: [PATCH 1/1] coresight: etm4x: Configure EL2 exception level when kernel is running in HYP

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Date:   Wed, 5 Sep 2018 14:34:36 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Tomasz Nowicki <tnowicki@...iumnetworks.com>
Cc:     alexander.shishkin@...ux.intel.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        coresight@...ts.linaro.org, Jayachandran.Nair@...ium.com,
        linux@...linux.org.uk
Subject: Re: [PATCH 1/1] coresight: etm4x: Configure EL2 exception level when
 kernel is running in HYP

Hi Tomasz,

On Tue, Sep 04, 2018 at 04:20:34PM +0200, Tomasz Nowicki wrote:
> For non-VHE systems host kernel runs at EL1 and jumps to EL2 whenever
> hypervisor code should be executed. In this case ETM4x driver must
> restrict configuration to EL1 when it setups kernel tracing.
> However, there is no separate hypervisor privilege level when VHE
> is enabled, the host kernel runs at EL2.
> 
> This patch fixes configuration of TRCACATRn register for VHE systems
> so that ETM_EXLEVEL_NS_HYP bit is used instead of ETM_EXLEVEL_NS_OS
> to on/off kernel tracing. At the same time, it moves common code
> to new helper.
> 
> Signed-off-by: Tomasz Nowicki <tnowicki@...iumnetworks.com>
> ---
>  drivers/hwtracing/coresight/coresight-etm4x.c | 39 ++++++++++---------
>  1 file changed, 20 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c b/drivers/hwtracing/coresight/coresight-etm4x.c
> index f79b0ea85d76..5f495c942f99 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x.c
> @@ -28,6 +28,7 @@
>  #include <linux/pm_runtime.h>
>  #include <asm/sections.h>
>  #include <asm/local.h>
> +#include <asm/virt.h>
>  
>  #include "coresight-etm4x.h"
>  #include "coresight-etm-perf.h"
> @@ -606,7 +607,7 @@ static void etm4_set_default_config(struct etmv4_config *config)
>  	config->vinst_ctrl |= BIT(0);
>  }
>  
> -static u64 etm4_get_access_type(struct etmv4_config *config)
> +static u64 etm4_get_ns_access_type(struct etmv4_config *config)
>  {
>  	u64 access_type = 0;
>  
> @@ -617,17 +618,27 @@ static u64 etm4_get_access_type(struct etmv4_config *config)
>  	 *   Bit[13] Exception level 1 - OS
>  	 *   Bit[14] Exception level 2 - Hypervisor
>  	 *   Bit[15] Never implemented
> -	 *
> -	 * Always stay away from hypervisor mode.
>  	 */
> -	access_type = ETM_EXLEVEL_NS_HYP;
>  

Extra space 

> -	if (config->mode & ETM_MODE_EXCL_KERN)
> -		access_type |= ETM_EXLEVEL_NS_OS;
> +	if (!is_kernel_in_hyp_mode()) {
> +		/* Stay away from hypervisor mode for non-VHE */
> +		access_type =  ETM_EXLEVEL_NS_HYP;
> +		if (config->mode & ETM_MODE_EXCL_KERN)
> +			access_type |= ETM_EXLEVEL_NS_OS;
> +	} else if (config->mode & ETM_MODE_EXCL_KERN) {
> +		access_type = ETM_EXLEVEL_NS_HYP;
> +	}
>  
>  	if (config->mode & ETM_MODE_EXCL_USER)
>  		access_type |= ETM_EXLEVEL_NS_APP;
>  
> +	return access_type;
> +}
> +
> +static u64 etm4_get_access_type(struct etmv4_config *config)
> +{
> +	u64 access_type = etm4_get_ns_access_type(config);
> +
>  	/*
>  	 * EXLEVEL_S, bits[11:8], don't trace anything happening
>  	 * in secure state.
> @@ -881,20 +892,10 @@ void etm4_config_trace_mode(struct etmv4_config *config)
>  
>  	addr_acc = config->addr_acc[ETM_DEFAULT_ADDR_COMP];
>  	/* clear default config */
> -	addr_acc &= ~(ETM_EXLEVEL_NS_APP | ETM_EXLEVEL_NS_OS);
> +	addr_acc &= ~(ETM_EXLEVEL_NS_APP | ETM_EXLEVEL_NS_OS |
> +			ETM_EXLEVEL_NS_HYP);

Indentation problems

>  
> -	/*
> -	 * EXLEVEL_NS, bits[15:12]
> -	 * The Exception levels are:
> -	 *   Bit[12] Exception level 0 - Application
> -	 *   Bit[13] Exception level 1 - OS
> -	 *   Bit[14] Exception level 2 - Hypervisor
> -	 *   Bit[15] Never implemented
> -	 */
> -	if (mode & ETM_MODE_EXCL_KERN)
> -		addr_acc |= ETM_EXLEVEL_NS_OS;
> -	else
> -		addr_acc |= ETM_EXLEVEL_NS_APP;
> +	addr_acc |= etm4_get_ns_access_type(config);
>  
>  	config->addr_acc[ETM_DEFAULT_ADDR_COMP] = addr_acc;
>  	config->addr_acc[ETM_DEFAULT_ADDR_COMP + 1] = addr_acc;

I tested your patch on my side and it didn't break kernel space decoding.

Since it would have taken longer to ask you to respin than to make the changes
myself, I applied your patch with the above modifications.

Thanks,
Mathieu

> -- 
> 2.17.1
>