Messages in this thread |  | | Date | Tue, 4 Oct 2016 17:10:57 -0600 | From | Jason Gunthorpe <> | Subject | Re: [PATCH] tpm: don't destroy chip device prematurely |
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On Tue, Oct 04, 2016 at 09:55:36PM +0000, Winkler, Tomas wrote: > > > On Tue, Oct 04, 2016 at 08:19:46AM +0300, Jarkko Sakkinen wrote: > > > > > > Make the driver uncallable first. The worst race that can happen is > > > > that open("/dev/tpm0", ...) returns -EPIPE. I do not consider this > > > > fatal at all. > > > > > > No responses for this reasonable proposal so I'll show what I mean: > > > > How is this any better than what Thomas proposed? It seems much worse to > > me since now we have even more stuff in the wrong order. > > > > There are three purposes to the ordering as it stands today > > 1) To guarantee that tpm2_shutdown is the last command delivered to > > the TPM. When it is issued all other ways to access the device > > are hard fenced off. > > I'm not sure where are you taking this requirements from simple bit > is just enough to make the HW inaccessible if the interface is > designed right.
I'm having a hard time understanding the english in your email. (Jarkko do you know what Tomas is talking about??)
> The ordering can be resolved, like this > > down_write(&chip->ops_sem); > if (chip->flags & TPM_CHIP_FLAG_TPM2) > tpm2_shutdown(chip, TPM2_SU_CLEAR); > up_write(&chip->ops_sem); > > device_del(&chip->dev); > > down_write(&chip->ops_sem); > chip->ops = NULL; > up_write(&chip->ops_sem);
No, that is wrong as well, another thread can issue a TPM command between the device_del and the ops = NULL. Presumably that will fail the same as tpm2_shutdown does.
> > I still haven't heard an explanation why Thomas's other patches need this, or > > why trying to change this ordering makes any sense at all considering how the > > subsystem is constructed. > > I thought it's quite clear form the commit message, the device_del
Not clear at all the commit message describes the 'solution' not the problem. This doesn't help..
> naturally toggles runtime_pm of the parent device, it tries to > resume the parent device so it can perform denationalization and > then suspend the parent device back which caused tpm2_shutdown to > fail.
What code actually fails? I don't see anything in the runtime pm patch that relies on chip->dev at all.
What code fails and why?
> I general we can not to implement power management via runtime_pm > and resolve the issue within tpm_crb driver but it's not abouth > tpm_crb. tpm2_shutdown is a tpm stack call it's not tpm_crb > function, it uses tpm_transmit_cmd and friends it should have valid > tpm_chip initialized and valid. I'm not sure what could be more > clearer than that.
I'll say it again, the tpm_transmit_cmd path must not require a registered chip->dev.
device_del only unregisters the dev, it does not deinitialize it, nor does it free any memory. I still don't understand how this has any impact on the pm stuff when all the pm stuff is attached only to the pdev.
> I have to admit that I'm not sure what the vtpm does yet, but I have > a feeling that a simple flag can fix this.
What flag? Fix what?
Jason
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