linux-kernel - RE: [xen vMCE RFC V0.2] xen vMCE design

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Message-Id: <4FEC7FB8020000780008C885@nat28.tlf.novell.com>
Date:	Thu, 28 Jun 2012 15:00:56 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Jinsong Liu" <jinsong.liu@...el.com>,
	"Will Auld" <will.auld@...el.com>
Cc:	"Ashok Raj" <ashok.raj@...el.com>,
	"Donald D Dugger" <donald.d.dugger@...el.com>,
	"Haitao Shan" <haitao.shan@...el.com>,
	"Jun Nakajima" <jun.nakajima@...el.com>,
	"Susie Li" <susie.li@...el.com>, "Tony Luck" <tony.luck@...el.com>,
	"Xiantao Zhang" <xiantao.zhang@...el.com>,
	"Yunhong Jiang" <yunhong.jiang@...el.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Keir Fraser" <keir@....org>
Subject: RE: [xen vMCE RFC V0.2] xen vMCE design

>>> On 28.06.12 at 15:38, "Liu, Jinsong" <jinsong.liu@...el.com> wrote:
> Jan Beulich wrote:
>>>>> On 28.06.12 at 11:40, "Liu, Jinsong" <jinsong.liu@...el.com> wrote:
>>> So I would like to push new vMCE as quickly as possible. What's the
>>> timeline of vMCE developing that xen 4.2 could accept?
>> 
>> Weeks ago, really. See
>> http://lists.xen.org/archives/html/xen-devel/2012-06/msg01619.html 
>> and follow-ups - we'd really only consider getting the save/restore 
>> interface into forward compatible shape as acceptable.
>> 
>>> I wonder if we could make major
>>> components of vMCE done before xen 4.2 timeline, and leave the
>>> surrounding features and the corner cases done later?
>> 
>> Unfortunately it's likely going to be even less. However, if split
>> that way, chances are things could go into e.g. 4.2.1.
>> 
>> Jan
> 
> So let's look at current vMCE status first:
> 1). functionally it work abnormally for guest (but tolerated by some guest 
> like linux/solaris);
> 2). before xen 4.1 it blocks migration when migrate from big bank to small 
> bank platform;

Before 4.2 you mean (in 4.1 we only have this as a backport in SLE11).

> We may try some middle steps, minimal adjusting for xen 4.2 release (to 
> avoid futher compatible issue at xen 4.2.1, 4.3, ...):
> 1). we don't handle vMCE function bugs, only make sure migration works OK;

That's the minimal goal.

> 2). update vMCE interface to a middle clean status:
>     * remove MCG_CTL (otherwise we have to add this useless MSR at new 
> vMCE);
>     * stick all 1's to MCi_CTL (avoid semantic difference);
>     * for MCG_CAP, clear MCG_CTL_P, limit to 2 banks (otherwise dirty code 
> have to be added at new vMCE);

Whether that's acceptable would need to be seen when code
is ready.

Jan

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