Re: FW: Wrt golden MMIO/CFG snaphot in GVT-g

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

On ti, 2016-05-31 at 22:01 +0800, Zhiyuan Lv wrote:
> Hi Joonas,
> 
> On Fri, May 27, 2016 at 02:32:25PM +0300, Joonas Lahtinen wrote:
> > 
> > On pe, 2016-05-27 at 10:05 +0000, Wang, Zhi A wrote:
> > > 
> > > For me I think maybe i915 could save the snapshot for GVT, then GVT-g 
> > > patch the snapshot itself, then there won’t be leaking happened I
> > > think. Even we wrote a dedicated little program, we would do the same
> > > thing.
> > >  
> > > From: Wang, Zhi A 
> > > Sent: Friday, May 27, 2016 12:59 PM
> > > To: joonas.lahtinen@linux.intel.com; 'Chris Wilson' ; Vetter, Daniel <daniel.vetter@intel.com>; tvrtko.ursulin@linux.intel.com
> > > Cc: Tian, Kevin <kevin.tian@intel.com>; Lv, Zhiyuan 
> > > Subject: Wrt golden MMIO/CFG snaphot in GVT-g
> > >  
> > > Hi Guys:
> > > I received some comments on from Kevin. Mostly his concern is the
> > > burden of maintain/releasing the MMIO/CFG snapshot for customers. As
> > > we might not have all the SKUs/platform which customers have, even we
> > > release the snapshot file generator for customer, it would still
> > > bring some extra effort when customer deploying the SW. And he
> > > suggested i915 better i915 could keep the snapshot for GVT-g during
> > > module loading.
> > It will be much harder to ask everyone else in addition to those with
> > odd hardware revisions to provide the boot-captured register state for
> > each bug they report. I do not feel adding some extra (one-time!)
> > effort for customers deploying on weird SKUs overcomes that everyone
> > would have to provide a register dump for each bug.
> The bug reporting/reproducing is a good point. We assume that in each
> driver load, the captured register state would be almost the same, and
> the difference won't bring difficulty for reproducing bugs.
> 
> Then we may not need register dump for each bug submission. Consider
> the case of an odd hardware, if we can find the same in hand, we could
> get the dump automatically. If we cannot find the same, even with the
> dump state from reporter, it still cannot guarantee the bug
> reproducing. We make VM to see identical MMIO state, but the real
> hardware state is different. Thanks!
> 

What benefits do we get from using the boot-up state?

I do not see any technical benefits, just avoiding one step for
customers with odd SKUs vs. all the benefits we would get from golden
state.

Regards, Joonas

> Regards,
> -Zhiyuan
> 
> > 
> > 
> > So I am still very much against making a register freeze at each boot.
> > Even creating a one-shot golden state automatically when one is found
> > missing the SKU from firmware package and then using that each time
> > would make the system operation more stable. It should not be too hard
> > to instruct customer to do that?
> 
> > 
> > 
> > Regards, Joonas
> > 
> > > 
> > > As we have shared some ideas about the security problem like leaking
> > > BIOS configuration to VM, better we could elaborate more ideas and
> > > figure out a better approach. Let’s discuss. J
> > >  
> > > Thanks,
> > > Zhi.
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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