Re: [RFC PATCH v12 3/4] hw/vfio/ap: Storing event information for an AP configuration change event

[Anthony Krowiak <akrowiak@linux.ibm.com>]

On 6/6/25 2:37 PM, Rorie Reyes wrote:
> These functions can be invoked by the function that handles interception
> of the CHSC SEI instruction for requests indicating the accessibility of
> one or more adjunct processors has changed.
>
> Signed-off-by: Rorie Reyes <rreyes@linux.ibm.com>

Reviewed-by: Anthony Krowiak <akrowiak@linux.ibm.com>

> ---
>   hw/vfio/ap.c                 | 43 ++++++++++++++++++++++++++++++++++++
>   include/hw/s390x/ap-bridge.h | 39 ++++++++++++++++++++++++++++++++
>   2 files changed, 82 insertions(+)
>
> diff --git a/hw/vfio/ap.c b/hw/vfio/ap.c
> index fc435f5c5b..7e3c6278b3 100644
> --- a/hw/vfio/ap.c
> +++ b/hw/vfio/ap.c
> @@ -10,6 +10,7 @@
>    * directory.
>    */
>   
> +#include <stdbool.h>
>   #include "qemu/osdep.h"
>   #include CONFIG_DEVICES /* CONFIG_IOMMUFD */
>   #include <linux/vfio.h>
> @@ -21,6 +22,7 @@
>   #include "hw/s390x/css.h"
>   #include "qemu/error-report.h"
>   #include "qemu/event_notifier.h"
> +#include "qemu/lockable.h"
>   #include "qemu/main-loop.h"
>   #include "qemu/module.h"
>   #include "qemu/option.h"
> @@ -48,6 +50,8 @@ typedef struct APConfigChgEvent {
>   static QTAILQ_HEAD(, APConfigChgEvent) cfg_chg_events =
>       QTAILQ_HEAD_INITIALIZER(cfg_chg_events);
>   
> +static QemuMutex cfg_chg_events_lock;
> +
>   OBJECT_DECLARE_SIMPLE_TYPE(VFIOAPDevice, VFIO_AP_DEVICE)
>   
>   static void vfio_ap_compute_needs_reset(VFIODevice *vdev)
> @@ -96,6 +100,38 @@ static void vfio_ap_cfg_chg_notifier_handler(void *opaque)
>   
>   }
>   
> +int ap_chsc_sei_nt0_get_event(void *res)
> +{
> +    ChscSeiNt0Res *nt0_res  = (ChscSeiNt0Res *)res;
> +    APConfigChgEvent *cfg_chg_event;
> +
> +    WITH_QEMU_LOCK_GUARD(&cfg_chg_events_lock) {
> +        if (QTAILQ_EMPTY(&cfg_chg_events)) {
> +            return EVENT_INFORMATION_NOT_STORED;
> +        }
> +
> +        cfg_chg_event = QTAILQ_FIRST(&cfg_chg_events);
> +        QTAILQ_REMOVE(&cfg_chg_events, cfg_chg_event, next);
> +    }
> +
> +    memset(nt0_res, 0, sizeof(*nt0_res));
> +    g_free(cfg_chg_event);
> +    nt0_res->flags |= PENDING_EVENT_INFO_BITMASK;
> +    nt0_res->length = sizeof(ChscSeiNt0Res);
> +    nt0_res->code = NT0_RES_RESPONSE_CODE;
> +    nt0_res->nt = NT0_RES_NT_DEFAULT;
> +    nt0_res->rs = NT0_RES_RS_AP_CHANGE;
> +    nt0_res->cc = NT0_RES_CC_AP_CHANGE;
> +
> +    return EVENT_INFORMATION_STORED;
> +}
> +
> +bool ap_chsc_sei_nt0_have_event(void)
> +{
> +    QEMU_LOCK_GUARD(&cfg_chg_events_lock);
> +    return !QTAILQ_EMPTY(&cfg_chg_events);
> +}
> +
>   static bool vfio_ap_register_irq_notifier(VFIOAPDevice *vapdev,
>                                             unsigned int irq, Error **errp)
>   {
> @@ -192,6 +228,13 @@ static void vfio_ap_realize(DeviceState *dev, Error **errp)
>       VFIOAPDevice *vapdev = VFIO_AP_DEVICE(dev);
>       VFIODevice *vbasedev = &vapdev->vdev;
>   
> +    static bool lock_initialized;
> +
> +    if (!lock_initialized) {
> +        qemu_mutex_init(&cfg_chg_events_lock);
> +        lock_initialized = true;
> +    }
> +
>       if (!vfio_device_get_name(vbasedev, errp)) {
>           return;
>       }
> diff --git a/include/hw/s390x/ap-bridge.h b/include/hw/s390x/ap-bridge.h
> index 470e439a98..7efc52928d 100644
> --- a/include/hw/s390x/ap-bridge.h
> +++ b/include/hw/s390x/ap-bridge.h
> @@ -16,4 +16,43 @@
>   
>   void s390_init_ap(void);
>   
> +typedef struct ChscSeiNt0Res {
> +    uint16_t length;
> +    uint16_t code;
> +    uint8_t reserved1;
> +    uint16_t reserved2;
> +    uint8_t nt;
> +#define PENDING_EVENT_INFO_BITMASK 0x80;
> +    uint8_t flags;
> +    uint8_t reserved3;
> +    uint8_t rs;
> +    uint8_t cc;
> +} QEMU_PACKED ChscSeiNt0Res;
> +
> +#define NT0_RES_RESPONSE_CODE 1
> +#define NT0_RES_NT_DEFAULT    0
> +#define NT0_RES_RS_AP_CHANGE  5
> +#define NT0_RES_CC_AP_CHANGE  3
> +
> +#define EVENT_INFORMATION_NOT_STORED 1
> +#define EVENT_INFORMATION_STORED     0
> +
> +/**
> + * ap_chsc_sei_nt0_get_event - Retrieve the next pending AP config
> + * change event
> + * @res: Pointer to a ChscSeiNt0Res struct to be filled with event
> + * data
> + *
> + * This function checks for any pending AP config change events and,
> + * if present, populates the provided response structure with the
> + * appropriate SEI NT0 fields.
> + *
> + * Return:
> + *   EVENT_INFORMATION_STORED - An event was available and written to @res
> + *   EVENT_INFORMATION_NOT_STORED - No event was available
> + */
> +int ap_chsc_sei_nt0_get_event(void *res);
> +
> +bool ap_chsc_sei_nt0_have_event(void);
> +
>   #endif