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


From: Jason J. Herne
Subject: Re: [Qemu-devel] [PATCH v4 00/15] s390: vfio-ccw dasd ipl support
Date: Mon, 11 Mar 2019 13:35:29 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1

On 3/11/19 1:33 PM, Cornelia Huck wrote:
On Mon, 11 Mar 2019 11:21:18 -0400
"Jason J. Herne" <address@hidden> 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 (address@hidden)




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