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List:       qemu-ppc
Subject:    Re: [Qemu-ppc] [PATCH v7 0/2] spapr-rtas: add ibm, get-vpd RTAS interface
From:       Greg Kurz <groug () kaod ! org>
Date:       2019-03-29 12:29:51
Message-ID: 20190329132951.451d4ef0 () bahia ! lan
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On Thu, 28 Mar 2019 15:39:45 -0300
"Maxiwell S. Garcia" <maxiwell@linux.ibm.com> wrote:

> Hi,
> 
> On Thu, Mar 28, 2019 at 02:21:51PM +0100, Greg Kurz wrote:
> > On Wed, 27 Mar 2019 17:41:00 -0300
> > "Maxiwell S. Garcia" <maxiwell@linux.ibm.com> wrote:
> >   
> > > Here are two patches to add a handler for ibm,get-vpd RTAS calls.
> > > This RTAS exposes host information in case of set QEMU options
> > > 'host-serial' and 'host-model' as 'passthrough'.
> > > 
> > > The patch 1 creates helper functions to get valid 'host-serial'
> > > and 'host-model' parameters, guided by QEMU command line. These
> > > parameters are useful to build the guest device tree and to return
> > > get-vpd RTAS calls. The patch 2 adds the ibm,get-vpd itself.
> > > 
> > > Update v7:
> > > * rtas_get_vpd_fields as a static array in spapr machine state
> > > 
> > > Maxiwell S. Garcia (2):
> > >   spapr: helper functions to get valid host fields
> > >   spapr-rtas: add ibm,get-vpd RTAS interface
> > > 
> > >  hw/ppc/spapr.c         | 48 +++++++++++----------
> > >  hw/ppc/spapr_rtas.c    | 96 ++++++++++++++++++++++++++++++++++++++++++
> > >  include/hw/ppc/spapr.h | 14 +++++-
> > >  3 files changed, 135 insertions(+), 23 deletions(-)
> > >   
> > 
> > Hi Maxiwell,
> > 
> > David sent a patch to rework how the host data is exposed to the guest.
> > Especially, the special casing of the "none" and "passthrough" strings
> > is no more... I'm afraid you'll have to rework your patches accordingly:
> > code+changelog in patch 1 and at least changelog in patch 2.
> > 
> > Cheers,  
> 
> IIUC, the 'ibm,get-vpd' RTAS should return information about the
> platform/cabinet. Thus, it's not necessary to add new nodes in the guest
> device tree to export information like that.

I agree that these "host-model" and "host-serial" props, which aren't
described anywhere and not used by either the linux kernel or the
powerpc-utils, look like a QEMU-specific poor man's version of VPD.

Not quite sure why they were even created since this is the purpose
of "system-id" and "model" as explained in PAPR, and supposedly
exposed in /proc/ppc64/lparcfg according to the LPARCFG(5) manual
page:

       serial_number
       The serial number of the physical system in which the partition resides

       system_type
       The  machine,type-model  of  the physical system in which the partition
       resides

This is indeed what we get in a PowerVM LPAR running on a tuleta system:

[root@furax1 ~]# head -3 /proc/ppc64/lparcfg 
lparcfg 1.9
serial_number=IBM,032116A9A
system_type=IBM,8247-22L

[root@furax1 ~]# echo $(cat /proc/device-tree/system-id)
IBM,032116A9A
[root@furax1 ~]# echo $(cat /proc/device-tree/model)
IBM,8247-22L

But QEMU generates a hard coded "IBM pSeries (emulated by qemu)" model,
which is clearly not PAPR compliant according to this requirement:

	R1–12.2–13. There must be a property, "model", under the root node
	in the format, "<vendor>,xxxx-yyy", where <vendor> is replaced by
	one to five letters representing the stock symbol of the company
	(for example, for IBM: "IBM,xxxx-yyy"), and where xxxx-yyy is
	derived from the VPD TM field (see Table 160‚ "LoPAPR VPD Fields‚"
	on page 343) of the first or ‘marked' processor enclosure.

And worse, it mixes "vm,uuid" which is QEMU specific concept to uniquely
identify guests, with "system-id" which is about the host :-\

All of this is very confusing and need to be sorted out before building
anything on top of it. Especially since "model" and "system-id" are
supposed to derive from VPD IIUC.

I guess that we should first decide what we really want to expose
in "system-id" and "model": what we have now ? the same as in
"host-serial" and "host-model", ie. user configurable ? Must we
stay compatible with existing setups ? In any case, I'm afraid that
we have to diverge from PAPR somehow, since it obviously doesn't
care about the security concerns that motivated recent changes
for "host-serial" and "host-model"...


> Since it's a POWER specific
> functionality, may 'ibm,get-vpd' export host information if the
> guest instance allows it? Or is it better return only the 'host-serial'
> and 'host-model' content, like in the patch "spapr: Simplify handling
> of host-serial and host-model values"?
> 

I've spent some time reading PAPR on this topic and I'm not sure that
"ibm,get-vpd" is the way to go for what you were trying to achieve
initially (ie, obtain up-to-date host model and serial after migration).

Have you looked at RTAS "ibm,update-properties" ?

	7.4.8 ibm,update-properties RTAS Call

	This RTAS call is used to report updates to the properties changed
	due to a massive platform reconfiguration such as when the partition
	is migrated between machines.

This explicitly covers updates to "system-id" and "model". Maybe it is
time to do as Ben was suggesting a long time ago when "host-serial"
and "host-model" were introduced [1]:

	On Tue, 2014-07-08 at 12:49 +0200, Alexander Graf wrote:
	> Please be aware that all of the above is bogus when you start
	> thinking 
	> about live migration.

	What's probably where we need to start thinking about implementing
	migration according to PAPR :-)

	IE. With pre and post-migration notifications to the guest including
	device-tree updates.

	Cheers,
	Ben.

[1] https://patchwork.ozlabs.org/patch/367792/#813547

Cheers,

--
Greg


> > 
> > --
> > Greg
> >   
> 
> 



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