linux-kernel - Re: [PATCH] s390: vfio-ap: trace the update of APCB masks

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Date:   Fri, 5 Oct 2018 09:50:58 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Pierre Morel <pmorel@...ux.ibm.com>
Cc:     borntraeger@...ibm.com, david@...hat.com,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, frankja@...ux.ibm.com, akrowiak@...ux.ibm.com,
        pasic@...ux.ibm.com
Subject: Re: [PATCH] s390: vfio-ap: trace the update of APCB masks

On Fri,  5 Oct 2018 09:33:01 +0200
Pierre Morel <pmorel@...ux.ibm.com> wrote:

> Define a tracing function to trace in the KVM trace buffer
> and trace the changes of the APCB masks.

In general, trace events are good :)

> 
> Signed-off-by: Pierre Morel <pmorel@...ux.ibm.com>
> ---
>  drivers/s390/crypto/vfio_ap_ops.c     | 22 ++++++++++++++++++++++
>  drivers/s390/crypto/vfio_ap_private.h |  4 ++++
>  2 files changed, 26 insertions(+)
> 
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> index a8a9984..00e632a 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -753,6 +753,28 @@ static void vfio_ap_mdev_copy_masks(struct ap_matrix_mdev *matrix_mdev)
>  	memcpy(aqm, matrix_mdev->matrix.aqm, nbytes);
>  	nbytes = DIV_ROUND_UP(matrix_mdev->matrix.adm_max + 1, BITS_PER_BYTE);
>  	memcpy(adm, matrix_mdev->matrix.adm, nbytes);
> +
> +	switch (matrix_mdev->kvm->arch.crypto.crycbd & CRYCB_FORMAT_MASK) {
> +	case CRYCB_FORMAT2:
> +		VM_AP_EVENT(matrix_mdev->kvm, 3,
> +			    "SET CRYCB: apm %016lx %016lx %016lx %016lx",
> +			    apm[0], apm[1], apm[2], apm[3]);
> +		VM_AP_EVENT(matrix_mdev->kvm, 3,
> +			    "SET CRYCB: aqm %016lx %016lx %016lx %016lx",
> +			    aqm[0], aqm[1], aqm[2], aqm[3]);
> +		VM_AP_EVENT(matrix_mdev->kvm, 3,
> +			    "SET CRYCB: adm %016lx %016lx %016lx %016lx",
> +			    adm[0], adm[1], adm[2], adm[3]);
> +		break;
> +	case CRYCB_FORMAT1:
> +	case CRYCB_FORMAT0: /* Both CRYCB format uses APCB format 0 */
> +	default: /* Can not happen */

If it can't happen, trace "SET CRYCB: invalid format '%x'" instead?

> +		VM_AP_EVENT(matrix_mdev->kvm, 3,
> +			    "SET CRYCB: apm %016lx aqm %04x adm %04x", apm[0],
> +			    *((unsigned short *)aqm), *((unsigned short *)adm));
> +		break;
> +	}
> +
>  }
>  
>  /**
> diff --git a/drivers/s390/crypto/vfio_ap_private.h b/drivers/s390/crypto/vfio_ap_private.h
> index 5675492..4cd779d 100644
> --- a/drivers/s390/crypto/vfio_ap_private.h
> +++ b/drivers/s390/crypto/vfio_ap_private.h
> @@ -19,6 +19,10 @@
>  
>  #include "ap_bus.h"
>  
> +#define VM_AP_EVENT(d_kvm, d_loglevel, d_string, d_args...)\
> +	debug_sprintf_event(d_kvm->arch.dbf, d_loglevel, d_string "\n", \
> +			    d_args)
> +
>  #define VFIO_AP_MODULE_NAME "vfio_ap"
>  #define VFIO_AP_DRV_NAME "vfio_ap"
>  

One thing I don't like about this is that you're using the kvm dbf from
driver code, which looks odd. OTOH, these are kvm-specific masks...

Is there anything else that you may want to trace in the vfio-ap
driver, so that you could add a dbf for it?