Message-ID: <20170123201646.GA72453@apronin>
Date:   Mon, 23 Jan 2017 12:16:46 -0800
From:   Andrey Pronin <apronin@...omium.org>
To:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:     linux-kernel@...r.kernel.org, semenzato@...omium.org,
        tpmdd-devel@...ts.sourceforge.net, groeck@...omium.org
Subject: Re: [tpmdd-devel] [PATCH] tpm/tpm_i2c_infineon: ensure no ongoing
 commands on shutdown

On Mon, Jan 23, 2017 at 12:02:46PM -0800, Andrey Pronin wrote:
> On Tue, Jan 17, 2017 at 04:22:07PM -0700, Jason Gunthorpe wrote:
> > On Tue, Jan 17, 2017 at 03:00:53PM -0800, Andrey Pronin wrote:
> > 
> > > Here I was talking not about tpm_tis_spi or tpm_tis. Those can
> > > continue relying on the core, or register the default handler using
> > > .shutdown = tpm_shutdown.  I'm talking about the driver like
> > > tpm_i2c_infineon, which although uses the core, is created for a
> > > specific family of chips. So, it can assume that it needs to send
> > > vendor-specific commands.
> > 
> > But this is exactly what I'm talking about, infineon chips come in
> > lots of interface types, and if their legacy i2c interface need a
> > vendor command then likely their chips that use a common interface do
> > as well.
> > 
> > Conflating interface and bus is something I have been ripping out over
> > the years..
> > 
> 
> Thanks, Jason. OK, I'll try to follow that path then with my patches.
> 
> > > > So, the core should detect chip XYZ and then issue the required
> > > > vendor-specific command in some way.
> > > 
> > > Do I get it right that you propose to create this new core tpm
> > > mechanism for handling shutdowns? I didn't find anything that'd
> > > allow to call vendor-specifc hooks from the core during shutdown,
> > > but may be I'm missing something.
> > 
> > It would be simple to add to the core path:
> > 
> > if (chip->id == 1234)
> >     tpm_vendor_1234_shutdown(...);
> > 
> > We don't need to involve the driver in this. If it becomes a very
> > complex thing down then road then we may need *bus* and *chip*
> > drivers, but for now the 'chip' driver(s) are just inlined in the core
> > code..
> > 
> > But if there is no actual need to do this right now then don't worry
> > about overdesigning things..
> 
> OK, I can live with chip->id specific logic in probe/shutdown, if that's
> the current approach.
> 
> > 
> > > > Probably the *best* thing would be to add shutdown to 'struct class'
> > > > in the driver core like suspend/resume?
> > > 
> > > Yes, if that could be added to struct class, and then device_shutdown()
> > > would call the class suspend, if the driver suspend is NULL, that'd
> > > solve it.
> > 
> > Won't know if it is possible until someone sends a patch to Greg/etc :)
> > 
> > > Then the core can register the default shutdown in class, and an
> > > individual access driver can override it by registering its own
> > > shutdown callback. Still, due to the ordering issues discussed
> > > above, it should be either/or, not first-driver-then-class, if both
> > > exist.
> > 
> > First class then driver is the usual model, which is OK for TPM.
> 
> If "first class then driver", then the already existing
> register_reboot_notifier() can play the role of the class handler,
> since those hooks are called before drivers' shutdown handlers.
> 
> > 
> > > So, we still need to export the common tpm_shutdown().
> > 
> > No need to export if no driver is calling it, like I said don't
> > overdesign here, it is trivial to change if someone needs to do
> > something different later.
> > 
> 
> So, I started putting together an alternative patch (decided to go
> with a new patch instead of a new version for this one, since it's
> no longer limited to Infineon driver). The new patch is just going
> to do the following
> 	down_write(&chip->ops_sem);
> 	if (chip->ops) {
> 		if (chip->flags & TPM_CHIP_FLAG_TPM2)
> 			tpm2_shutdown(chip, TPM2_SU_CLEAR);
> 		chip->ops = NULL;
> 	}
> 	up_write(&chip->ops_sem);
> on shutdown in registered "reboot notifier".
> 
> I went through the places that access chip->ops to see what's
> going on at the moment with protecting them with tpm_try_get_ops().
> Here is the current state:
> 
>  - tpm_transmit/tpm_transmit_cmd. Not exported and are only called
>    by the core after tpm_try_get_ops() except for one place in
>    sysfs - pubek_show().
> 
>  - sysfs also directly accesses chip->ops in cancel_store(), but
>    that routine doesn't seem to be used anywhere. Shall it be
>    just removed?

My bad, need more coffee. Of course, cancel_store() is used. So, should
fix that as well.

> 
>  - tpm_get_timeouts. Besides the core is called by xen-tpmfront,
>    but before tpm_chip_register(), so no harm possible as of now.
> 
>  - wait_for_tpm_stat. Besides the core is called by xen-tpmfront.
>    It is called from inside chip->ops handlers only, which presumably
>    can happen only when the ops_sem is hold (once sysfs is fixed).
> 
>  - st33zp24 has it's own wait_for_stat() function that goes directly
>    to chip->ops. It happens inside chip->ops->recv/send (as for Xen),
>    which is fine. And also inside its resume handler, which is fine
>    as long as resume can never happen after shutdown (I believe it's
>    true).
> 
> So, if I add going through tpm_try_get_ops() to pubek_show and
> delete cancel_store(), that'll fix sysfs, and be enough for the things
> to work for now.
> 
> But it looks a bit brittle. So, before I submit my next patch:
> Do you think it's ok to leave wait_for_tpm_stat() and
> tpm_get_timeouts() and just continue be mindful when using those
> low-level functions? Or, shall we instead move acquiring ops_sem
> and checking for ops == NULL inside those low-level functions:
> tpm_transmit, wait_for_tpm_stat, tpm_get_timeout. It then should
> probably be separated from get_device(), which can be kept inside
> tpm_try_get_ops().
> 
> > > to start with that: create and export the common tpm_shutdown() from
> > > the core, that send Shutdown(CLEAR) for 2.0 and null-ifies chip->ops
> > > (and fix sysfs to acquire chip->ops_sem) and let the interested drivers
> > > call it.
> > 
> > I think you should do this and use the reboot_notifier or
> > class->shutdown approach
> > 
> > I'm not completely sure why you are worrying about sending a
> > vendor-specific command at shutdown. Do you actually need that?
> >
> 
> Yes, I do need that to send sleep-control vendor commands to the
> device in my case during shutdown (as well as suspend and resume).
> It makes much more sense to send them using tpm_transfer_cmd, which
> relies on chip->ops, than reimplementing the same functionality in
> the device driver.
> 
> Again, I can live with "if (chip->id == 1234)" logic in core to
> achieve that for now, if that's the chosen course. (Or, just
> register a device-specific "reboot notifier" with lower priority
> to be called before the "class-level" shutdown logic.)
> 
> > 
> > Jason
> 
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