Message-ID: <20250806121026.000023fe@huawei.com>
Date: Wed, 6 Aug 2025 12:10:26 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: <dan.j.williams@...el.com>
CC: <linux-coco@...ts.linux.dev>, <linux-pci@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <bhelgaas@...gle.com>, <aik@....com>,
	<lukas@...ner.de>, Samuel Ortiz <sameo@...osinc.com>, Xu Yilun
	<yilun.xu@...ux.intel.com>
Subject: Re: [PATCH v4 04/10] PCI/TSM: Authenticate devices via platform TSM


> >   
> > > diff --git a/drivers/pci/tsm.c b/drivers/pci/tsm.c
> > > new file mode 100644
> > > index 000000000000..0784cc436dd3
> > > --- /dev/null
> > > +++ b/drivers/pci/tsm.c
> > > @@ -0,0 +1,554 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +/*
> > > + * TEE Security Manager for the TEE Device Interface Security Protocol
> > > + * (TDISP, PCIe r6.1 sec 11)
> > > + *
> > > + * Copyright(c) 2024 Intel Corporation. All rights reserved.
> > > + */  
> >   
> > > +static void tsm_remove(struct pci_tsm *tsm)
> > > +{
> > > +	struct pci_dev *pdev;
> > > +
> > > +	if (!tsm)  
> > 
> > You protect against this in the DEFINE_FREE() so probably safe
> > to assume it is always set if we get here.  
> 
> It is safe, but I would rather not require reading other code to
> understand the expectation that some callers may unconditionally call
> this routine.

I think a function like remove being called on 'nothing' should
pretty much always be a bug, but meh, up to you.

> 
> > > +		return;
> > > +
> > > +	pdev = tsm->pdev;
> > > +	tsm->ops->remove(tsm);
> > > +	pdev->tsm = NULL;
> > > +}
> > > +DEFINE_FREE(tsm_remove, struct pci_tsm *, if (_T) tsm_remove(_T))
> > > +
> > > +static int call_cb_put(struct pci_dev *pdev, void *data,  
> > 
> > Is this combination worth while?  I don't like the 'and' aspect of it
> > and it only saves a few lines...
> > 
> > vs
> > 	if (pdev) {
> > 		rc = cb(pdev, data);
> > 		pci_dev_put(pdev);
> > 		if (rc)
> > 			return;
> > 	}  
> 
> I think it is worth it, but an even better option is to just let
> scope-based cleanup handle it by moving the variable inside the loop
> declaration.
I don't follow that lat bit, but will look at next version to see
what you mean!

> 

> > > +                return;
> > > +
> > > +        if (!is_dsm(pdev))
> > > +                return;
> > > +
> > > +        pci_walk_bus(pdev->subordinate, cb, data);
> > > +}
> > > +
> >   
> > > +/*
> > > + * Find the PCI Device instance that serves as the Device Security
> > > + * Manger (DSM) for @pdev. Note that no additional reference is held for
> > > + * the resulting device because @pdev always has a longer registered
> > > + * lifetime than its DSM by virtue of being a child of or identical to
> > > + * its DSM.
> > > + */
> > > +static struct pci_dev *find_dsm_dev(struct pci_dev *pdev)
> > > +{
> > > +	struct pci_dev *uport_pf0;
> > > +
> > > +	if (is_pci_tsm_pf0(pdev))
> > > +		return pdev;
> > > +
> > > +	struct pci_dev *pf0 __free(pci_dev_put) = pf0_dev_get(pdev);
> > > +	if (!pf0)
> > > +		return NULL;
> > > +
> > > +	if (is_dsm(pf0))
> > > +		return pf0;  
> > 
> > 
> > Unusual for a find command to not hold the device reference on the device
> > it returns.  Maybe just call that out in the comment.  
> 
> It is, "Note that no additional reference..."

Good point :)

> > > diff --git a/drivers/virt/coco/tsm-core.c b/drivers/virt/coco/tsm-core.c
> > > index 1f53b9049e2d..093824dc68dd 100644
> > > --- a/drivers/virt/coco/tsm-core.c
> > > +++ b/drivers/virt/coco/tsm-core.c  

> > > +static struct tsm_dev *tsm_register_pci_or_reset(struct tsm_dev *tsm_dev,
> > > +						 struct pci_tsm_ops *pci_ops)
> > > +{
> > > +	int rc;
> > > +
> > > +	if (!pci_ops)
> > > +		return tsm_dev;
> > > +
> > > +	pci_ops->owner = tsm_dev;
> > > +	tsm_dev->pci_ops = pci_ops;
> > > +	rc = pci_tsm_register(tsm_dev);
> > > +	if (rc) {
> > > +		dev_err(tsm_dev->dev.parent,
> > > +			"PCI/TSM registration failure: %d\n", rc);
> > > +		device_unregister(&tsm_dev->dev);  
> > 
> > As below. I'm fairly sure this device_unregister is nothing to do with
> > what this function is doing, so having it buried in here is less easy
> > to follow than pushing it up a layer.  
> 
> I prefer a short function with an early exit and no scope based unwind
> for this.
> 
> > > +		return ERR_PTR(rc);
> > > +	}
> > > +
> > > +	/* Notify TSM userspace that PCI/TSM operations are now possible */
> > > +	kobject_uevent(&tsm_dev->dev.kobj, KOBJ_CHANGE);
> > > +	return tsm_dev;
> > > +}
> > > +
> > >  static void put_tsm_dev(struct tsm_dev *tsm_dev)
> > >  {
> > >  	if (!IS_ERR_OR_NULL(tsm_dev))
> > > @@ -54,7 +109,8 @@ DEFINE_FREE(put_tsm_dev, struct tsm_dev *,
> > >  	    if (!IS_ERR_OR_NULL(_T)) put_tsm_dev(_T))
> > >  
> > >  struct tsm_dev *tsm_register(struct device *parent,
> > > -			     const struct attribute_group **groups)
> > > +			     const struct attribute_group **groups,
> > > +			     struct pci_tsm_ops *pci_ops)
> > >  {
> > >  	struct tsm_dev *tsm_dev __free(put_tsm_dev) =
> > >  		alloc_tsm_dev(parent, groups);
> > > @@ -73,12 +129,13 @@ struct tsm_dev *tsm_register(struct device *parent,
> > >  	if (rc)
> > >  		return ERR_PTR(rc);
> > >  
> > > -	return no_free_ptr(tsm_dev);
> > > +	return tsm_register_pci_or_reset(no_free_ptr(tsm_dev), pci_ops);  
> > 
> > Having a function call that either succeeds or cleans up something it
> > never did on error is odd.  
> 
> devm_add_action_or_reset() is the same pattern. Do the action, or
> otherwise take care of cleaning up. The action in this case is
> pci_tsm_register() and the reset is cleaning up the device_add().

It's a pretty obscure pattern but I agree there is that precedence.
In my head that one case gets to be 'special' because it is always
calling the callback, just a question of now or later (in remove).
Here thing callback happens in remove but it's explicit and nothing
to do with this function (unlikely the devm version)

Anyhow, not a thing I'm going to bother pushing back that hard on.
> 
> 
> > The or_reset hints at that oddity but to me is not enough. If you want
> > to use __free magic in here maybe hand off the tsm_dev on succesful
> > device registration.
> > 
> > 	struct tsm_dev *registered_tsm_dev __free(unregister_tsm_dev) =
> > 		no_free_ptr(tsm_dev);  
> 
> That does not look like an improvement to me.
> 
> The moment device_add() succeeds the cleanup shifts from put_device() to
> device_unregister(). I considered wrapping device_add(), but I think it
> is awkard to redeclare the same variable again vs being able to walk all
> instances of @tsm_dev in the function.

I agree it's a slightly odd construction and so might cause confusion.
So whilst I think I prefer it to the or_reset() pattern I guess I'll just
try and remember why this is odd (should I ever read this again after it's
merged!) :)

> 
> [..]
> > > + * struct pci_tsm_ops - manage confidential links and security state
> > > + * @link_ops: Coordinate PCIe SPDM and IDE establishment via a platform TSM.
> > > + * 	      Provide a secure session transport for TDISP state management
> > > + * 	      (typically bare metal physical function operations).
> > > + * @sec_ops: Lock, unlock, and interrogate the security state of the
> > > + *	     function via the platform TSM (typically virtual function
> > > + *	     operations).
> > > + * @owner: Back reference to the TSM device that owns this instance.
> > > + *
> > > + * This operations are mutually exclusive either a tsm_dev instance
> > > + * manages phyiscal link properties or it manages function security
> > > + * states like TDISP lock/unlock.
> > > + */
> > > +struct pci_tsm_ops {
> > > +	/*  
> > Likewise though I'm not sure if kernel-doc deals with struct groups.  
> 
> It does not.

Hmm. Given they are getting common maybe that's one to address, but
obviously not in this series.

Jonathan

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