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Date: Thu, 23 May 2013 16:58:05 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] qemu seabios issue with vhost-scsi
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To: Badari Pulavarty <pbadari@us.ibm.com>
Cc: Stefan Hajnoczi <stefanha@gmail.com>, Asias He <asias@redhat.com>, qemu-devel <qemu-devel@nongnu.org>, "Nicholas A. Bellinger" <nab@linux-iscsi.org>, Gleb Natapov <gleb@redhat.com>

Il 23/05/2013 16:48, Badari Pulavarty ha scritto:
>> The common virtio-scsi code in QEMU should guard against this.  In
>> virtio-blk data plane I hit a similar case and ended up starting the
>> data plane thread (equivalent to vhost here) *before* the status
>> register is set to DRIVER_OK.
> 
> Thats exactly what my debug in vhost_scsi_set_status() shows.
> 
> set status started 0 val 0
> set status started 0 val 0
> set status started 0 val 0
> set status started 0 val 0
> set status started 0 val 0
> set status started 0 val 3
> Program received signal SIGSEGV, Segmentation fault.
> 
> We never got a chance to call vhost_scsi_start() as we are waiting
> for DRIVER_OK.

This is the fix in SeaBIOS:

commit 5a7730db57ab0715223421e65b54fb50d6fefe5c
Author: Asias He <asias@redhat.com>
Date:   Fri Mar 15 09:45:15 2013 +0800

    virtio-scsi: Set _DRIVER_OK flag before scsi target scanning

    Before we start scsi target scanning, we need to set the
    VIRTIO_CONFIG_S_DRIVER_OK flag so the device can do setup properly.

    This fix a bug when booting tcm_vhost with seabios.

    Signed-off-by: Asias He <asias@redhat.com>
    Acked-by: Paolo Bonzini <pbonzini@redhat.com>



Still, Gleb is right that SeaBIOS should not be able to crash QEMU;
exit(1) is fine, SIGSEGV is not.

Paolo