Re: [PATCH v1 04/15] nitro_enclaves: Init PCI device driver

[Paraschiv, Andra-Irina]

On 25/04/2020 17:25, Liran Alon wrote:
> On 21/04/2020 21:41, Andra Paraschiv wrote:
> > +
> > +/**
> > + * ne_setup_msix - Setup MSI-X vectors for the PCI device.
> > + *
> > + * @pdev: PCI device to setup the MSI-X for.
> > + * @ne_pci_dev: PCI device private data structure.
> > + *
> > + * @returns: 0 on success, negative return value on failure.
> > + */
> > +static int ne_setup_msix(struct pci_dev *pdev, struct ne_pci_dev 
> > *ne_pci_dev)
> > +{
> > +ÂÂÂ int nr_vecs = 0;
> > +ÂÂÂ int rc = -EINVAL;
> > +
> > +ÂÂÂ BUG_ON(!ne_pci_dev);
> This kind of defensive programming does not align with Linux coding 
> convention.
> I think these BUG_ON() conditions should be removed.

I replaced with WARN_ON here and in the other places in the codebase.

> > +
> > +ÂÂÂ nr_vecs = pci_msix_vec_count(pdev);
> > +ÂÂÂ if (nr_vecs < 0) {
> > +ÂÂÂÂÂÂÂ rc = nr_vecs;
> > +
> > +ÂÂÂÂÂÂÂ dev_err_ratelimited(&pdev->dev,
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ "Failure in getting vec count [rc=%d]\n",
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ rc);
> > +
> > +ÂÂÂÂÂÂÂ return rc;
> > +ÂÂÂ }
> > +
> > +ÂÂÂ rc = pci_alloc_irq_vectors(pdev, nr_vecs, nr_vecs, PCI_IRQ_MSIX);
> > +ÂÂÂ if (rc < 0) {
> > +ÂÂÂÂÂÂÂ dev_err_ratelimited(&pdev->dev,
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ "Failure in alloc MSI-X vecs [rc=%d]\n",
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ rc);
> > +
> > +ÂÂÂÂÂÂÂ goto err_alloc_irq_vecs;
> You should just replace this with "return rc;" as no cleanup is 
> required here.

Done.

> > +ÂÂÂ }
> > +
> > +ÂÂÂ return 0;
> > +
> > +err_alloc_irq_vecs:
> > +ÂÂÂ return rc;
> > +}
> > +
> > +/**
> > + * ne_pci_dev_enable - Select PCI device version and enable it.
> > + *
> > + * @pdev: PCI device to select version for and then enable.
> > + * @ne_pci_dev: PCI device private data structure.
> > + *
> > + * @returns: 0 on success, negative return value on failure.
> > + */
> > +static int ne_pci_dev_enable(struct pci_dev *pdev,
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ struct ne_pci_dev *ne_pci_dev)
> > +{
> > +ÂÂÂ u8 dev_enable_reply = 0;
> > +ÂÂÂ u16 dev_version_reply = 0;
> > +
> > +ÂÂÂ BUG_ON(!pdev);
> > +ÂÂÂ BUG_ON(!ne_pci_dev);
> > +ÂÂÂ BUG_ON(!ne_pci_dev->iomem_base);
> Same.
> > +
> > +ÂÂÂ iowrite16(NE_VERSION_MAX, ne_pci_dev->iomem_base + NE_VERSION);
> > +
> > +ÂÂÂ dev_version_reply = ioread16(ne_pci_dev->iomem_base + NE_VERSION);
> > +ÂÂÂ if (dev_version_reply != NE_VERSION_MAX) {
> > +ÂÂÂÂÂÂÂ dev_err_ratelimited(&pdev->dev,
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ "Failure in pci dev version cmd\n");
> > +
> > +ÂÂÂÂÂÂÂ return -EIO;
> > +ÂÂÂ }
> > +
> > +ÂÂÂ iowrite8(NE_ENABLE_ON, ne_pci_dev->iomem_base + NE_ENABLE);
> > +
> > +ÂÂÂ dev_enable_reply = ioread8(ne_pci_dev->iomem_base + NE_ENABLE);
> > +ÂÂÂ if (dev_enable_reply != NE_ENABLE_ON) {
> > +ÂÂÂÂÂÂÂ dev_err_ratelimited(&pdev->dev,
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ "Failure in pci dev enable cmd\n");
> > +
> > +ÂÂÂÂÂÂÂ return -EIO;
> > +ÂÂÂ }
> > +
> > +ÂÂÂ return 0;
> > +}
> > +
> > +/**
> > + * ne_pci_dev_disable - Disable PCI device.
> > + *
> > + * @pdev: PCI device to disable.
> > + * @ne_pci_dev: PCI device private data structure.
> > + *
> > + * @returns: 0 on success, negative return value on failure.
> > + */
> > +static int ne_pci_dev_disable(struct pci_dev *pdev,
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ struct ne_pci_dev *ne_pci_dev)
> > +{
> > +ÂÂÂ u8 dev_disable_reply = 0;
> > +
> > +ÂÂÂ BUG_ON(!pdev);
> > +ÂÂÂ BUG_ON(!ne_pci_dev);
> > +ÂÂÂ BUG_ON(!ne_pci_dev->iomem_base);
> Same.
> > +
> > +ÂÂÂ iowrite8(NE_ENABLE_OFF, ne_pci_dev->iomem_base + NE_ENABLE);
> > +
> > +ÂÂÂ /*
> > +ÂÂÂÂ * TODO: Check for NE_ENABLE_OFF in a loop, to handle cases when 
> > the
> > +ÂÂÂÂ * device state is not immediately set to disabled and going 
> > through a
> > +ÂÂÂÂ * transitory state of disabling.
> > +ÂÂÂÂ */
> > +ÂÂÂ dev_disable_reply = ioread8(ne_pci_dev->iomem_base + NE_ENABLE);
> > +ÂÂÂ if (dev_disable_reply != NE_ENABLE_OFF) {
> > +ÂÂÂÂÂÂÂ dev_err_ratelimited(&pdev->dev,
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ "Failure in pci dev disable cmd\n");
> > +
> > +ÂÂÂÂÂÂÂ return -EIO;
> > +ÂÂÂ }
> > +
> > +ÂÂÂ return 0;
> > +}
> > +
> > +static int ne_probe(struct pci_dev *pdev, const struct pci_device_id 
> > *id)
> > +{
> > +ÂÂÂ struct ne_pci_dev *ne_pci_dev = NULL;
> > +ÂÂÂ int rc = -EINVAL;
> Unnecessary variable initialization.
> ne_pci_dev and rc are initialized below always before they are used.

I would rather keep the initialization in place overall, to not have a 
mix of init and uninit vars, when needed.

> > +
> > +ÂÂÂ ne_pci_dev = kzalloc(sizeof(*ne_pci_dev), GFP_KERNEL);
> > +ÂÂÂ if (!ne_pci_dev)
> > +ÂÂÂÂÂÂÂ return -ENOMEM;
> > +
> > +ÂÂÂ rc = pci_enable_device(pdev);
> > +ÂÂÂ if (rc < 0) {
> > +ÂÂÂÂÂÂÂ dev_err_ratelimited(&pdev->dev,
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ "Failure in pci dev enable [rc=%d]\n", rc);
> > +
> Why is this dev_err_ratelimited() instead of dev_err()?
> Same for the rest of error printing in this probe() method and other 
> places in this patch.

Just to avoid any misbehaving scenario, where would be way too many logs 
in a short timeframe. Here may not happen, but while handling PCI dev 
requests could be.

> > +ÂÂÂÂÂÂÂ goto err_pci_enable_dev;
> I find it confusing that the error labels are named based on the 
> failure-case they are used,
> instead of the action they do (i.e. Unwind previous successful 
> operation that requires unwinding).
> This doesn't seem to match Linux kernel coding convention.
> It also created an unnecessary 2 labels pointing to the same place in 
> cleanup code.

Yep, that's better this way wrt the naming of the labels. I updated the 
gotos in the patch series.

> > +ÂÂÂ }
> > +
> > +ÂÂÂ rc = pci_request_regions_exclusive(pdev, "ne_pci_dev");
> > +ÂÂÂ if (rc < 0) {
> > +ÂÂÂÂÂÂÂ dev_err_ratelimited(&pdev->dev,
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ "Failure in pci request regions [rc=%d]\n",
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ rc);
> > +
> > +ÂÂÂÂÂÂÂ goto err_req_regions;
> > +ÂÂÂ }
> > +
> > +ÂÂÂ ne_pci_dev->iomem_base = pci_iomap(pdev, PCI_BAR_NE, 0);
> > +ÂÂÂ if (!ne_pci_dev->iomem_base) {
> > +ÂÂÂÂÂÂÂ rc = -ENOMEM;
> > +
> > +ÂÂÂÂÂÂÂ dev_err_ratelimited(&pdev->dev,
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ "Failure in pci bar mapping [rc=%d]\n", rc);
> > +
> > +ÂÂÂÂÂÂÂ goto err_iomap;
> > +ÂÂÂ }
> > +
> > +ÂÂÂ rc = ne_setup_msix(pdev, ne_pci_dev);
> > +ÂÂÂ if (rc < 0) {
> > +ÂÂÂÂÂÂÂ dev_err_ratelimited(&pdev->dev,
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ "Failure in pci dev msix setup [rc=%d]\n",
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ rc);
> > +
> > +ÂÂÂÂÂÂÂ goto err_setup_msix;
> > +ÂÂÂ }
> > +
> > +ÂÂÂ rc = ne_pci_dev_disable(pdev, ne_pci_dev);
> > +ÂÂÂ if (rc < 0) {
> > +ÂÂÂÂÂÂÂ dev_err_ratelimited(&pdev->dev,
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ "Failure in ne_pci_dev disable [rc=%d]\n",
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ rc);
> > +
> > +ÂÂÂÂÂÂÂ goto err_ne_pci_dev_disable;
> > +ÂÂÂ }
> It seems weird that we need to disable the device before enabling it 
> on the probe() method.
> Why can't we just enable the device without disabling it?

The pci dev disable call cleanups the internal state of the device and 
terminates any running / "dangling" enclaves; here it is included just 
in case any remaining state from a previous PCI device use. The below 
enable call would fail in that case, though.

> > +
> > +ÂÂÂ rc = ne_pci_dev_enable(pdev, ne_pci_dev);
> > +ÂÂÂ if (rc < 0) {
> > +ÂÂÂÂÂÂÂ dev_err_ratelimited(&pdev->dev,
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ "Failure in ne_pci_dev enable [rc=%d]\n",
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ rc);
> > +
> > +ÂÂÂÂÂÂÂ goto err_ne_pci_dev_enable;
> > +ÂÂÂ }
> > +
> > +ÂÂÂ atomic_set(&ne_pci_dev->cmd_reply_avail, 0);
> > +ÂÂÂ init_waitqueue_head(&ne_pci_dev->cmd_reply_wait_q);
> > +ÂÂÂ INIT_LIST_HEAD(&ne_pci_dev->enclaves_list);
> > +ÂÂÂ mutex_init(&ne_pci_dev->enclaves_list_mutex);
> > +ÂÂÂ mutex_init(&ne_pci_dev->pci_dev_mutex);
> > +
> > +ÂÂÂ pci_set_drvdata(pdev, ne_pci_dev);
> If you would have pci_set_drvdata() as one of the first operations in 
> ne_probe(), then you could have avoided
> passing both struct pci_dev and struct ne_pci_dev parameters to 
> ne_setup_msix(), ne_pci_dev_enable() and ne_pci_dev_disable().
> Which would have been a bit more elegant.

Fair point. I moved pci_set_drvdata() upper in the logic and updated the 
signature of the functions to only include the pci_dev parameter.

> > +
> > +ÂÂÂ return 0;
> > +
> > +err_ne_pci_dev_enable:
> > +err_ne_pci_dev_disable:
> > +ÂÂÂ pci_free_irq_vectors(pdev);
> > +err_setup_msix:
> > +ÂÂÂ pci_iounmap(pdev, ne_pci_dev->iomem_base);
> > +err_iomap:
> > +ÂÂÂ pci_release_regions(pdev);
> > +err_req_regions:
> > +ÂÂÂ pci_disable_device(pdev);
> > +err_pci_enable_dev:
> > +ÂÂÂ kzfree(ne_pci_dev);
> An empty new-line is appropriate here.
> To separate the return statement from the cleanup logic.

Done.

> > +ÂÂÂ return rc;
> > +}
> > +
> > +static void ne_remove(struct pci_dev *pdev)
> > +{
> > +ÂÂÂ struct ne_pci_dev *ne_pci_dev = pci_get_drvdata(pdev);
> > +
> > +ÂÂÂ if (!ne_pci_dev || !ne_pci_dev->iomem_base)
> > +ÂÂÂÂÂÂÂ return;
> Why is this condition necessary?
> The ne_remove() function should be called only in case ne_probe() 
> succeeded.
> In that case, both ne_pci_dev and ne_pci_dev->iomem_base should be 
> non-NULL.

Correct, that shouldn't happen.

Just for early exit in case of bad behavior.

> > +
> > +ÂÂÂ ne_pci_dev_disable(pdev, ne_pci_dev);
> > +
> > +ÂÂÂ pci_set_drvdata(pdev, NULL);
> > +
> > +ÂÂÂ pci_free_irq_vectors(pdev);
> > +
> > +ÂÂÂ pci_iounmap(pdev, ne_pci_dev->iomem_base);
> > +
> > +ÂÂÂ kzfree(ne_pci_dev);
> > +
> > +ÂÂÂ pci_release_regions(pdev);
> > +
> > +ÂÂÂ pci_disable_device(pdev);
> You should aspire to keep ne_remove() order of operations to be the 
> reverse order of operations done in ne_probe().
> Which would also nicely match the order of operations done in 
> ne_probe() cleanup.
> i.e. The following order:
>
> pci_set_drvdata();
> ne_pci_dev_disable();
> pci_free_irq_vectors();
> pci_iounmap();
> pci_release_regions();
> pci_disable_device()
> kzfree();

I updated the order of operations.


Thanks for review, Liran.

Andra





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