Re: [Qemu-devel] [PATCH v4 00/15] s390: vfio-ccw dasd ipl support

["Jason J. Herne" <jjherne@linux.ibm.com>]

On 3/11/19 1:33 PM, Cornelia Huck wrote:
> On Mon, 11 Mar 2019 11:21:18 -0400
> "Jason J. Herne" <jjherne@linux.ibm.com> wrote:
> 
>> This is to support booting from vfio-ccw dasd devices. We basically implement
>> the real hardware ipl procedure. This allows for booting Linux guests on
>> vfio-ccw devices.
>>
>> vfio-ccw's channel program prefetch algorithm complicates ipl because most ipl
>> channel programs dynamically modify themselves. Details on the ipl process and
>> how we worked around this issue can be found in docs/devel/s390-dasd-ipl.txt.
>>
>> *********************
>> NOTE: Newer DASD units which initially present as control unit type 3990 may in
>> fact really be 2107. Some operating systems may enable 2107 features for these
>> devices thereby making sense id return a control unit type of 2107. I've added
>> support for control unit type 2107 so we can ipl from these devices.
>> *********************
> 
> Ugh. I'd have hoped that would have been recognized as A Bad Idea the
> last time we had a design like that...
> 
> Does that cu type switch persist over subchannel enable/disable?
> Subsystem reset?

It persists over a disable/enable, but not a reset it seems.

-- 
-- Jason J. Herne (jjherne@linux.ibm.com)