Re: [Qemu-devel] [PATCH 05/10] hyperv: add synic message delivery

[Paolo Bonzini]

On 21/09/2018 10:22, Roman Kagan wrote:
> +typedef struct HvSintStagedMesage {
> +    /* message content staged by hyperv_post_msg */
> +    struct hyperv_message msg;
> +    /* callback + data (r/o) to complete the processing in a BH */
> +    HvSintMsgCb cb;
> +    void *cb_data;
> +    /* message posting status filled by cpu_post_msg */
> +    int status;
> +    /* passing the buck: */
> +    enum {
> +        /* initial state */
> +        HV_STAGED_MSG_FREE,
> +        /*
> +         * hyperv_post_msg (e.g. in main loop) grabs the staged area (FREE ->
> +         * BUSY), copies msg, and schedules cpu_post_msg on the assigned cpu
> +         */
> +        HV_STAGED_MSG_BUSY,
> +        /*
> +         * cpu_post_msg (vcpu thread) tries to copy staged msg to msg slot,
> +         * notify the guest, records the status, marks the posting done (BUSY
> +         * -> POSTED), and schedules sint_msg_bh BH
> +         */
> +        HV_STAGED_MSG_POSTED,
> +        /*
> +         * sint_msg_bh (BH) verifies that the posting is done, runs the
> +         * callback, and starts over (POSTED -> FREE)
> +         */
> +    } state;
> +} HvSintStagedMesage;

s/Mesage/Message/

> +    if (atomic_read(&staged_msg->state) != HV_STAGED_MSG_POSTED) {
> +        /* status nor ready yet (spurious ack from guest?), ignore */
> +        return;
> +    }
> +

Can this actually happen?  It seems scary...

Paolo