linux-kernel - Re: [PATCH V16 3/6] PCI/DOE: Add DOE mailbox support functions

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Date:   Tue, 25 Oct 2022 12:03:15 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     <ira.weiny@...el.com>
CC:     Dan Williams <dan.j.williams@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Li, Ming" <ming4.li@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Lukas Wunner <lukas@...ner.de>,
        Alison Schofield <alison.schofield@...el.com>,
        "Vishal Verma" <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        "Ben Widawsky" <bwidawsk@...nel.org>,
        <linux-kernel@...r.kernel.org>, <linux-cxl@...r.kernel.org>,
        <linux-pci@...r.kernel.org>,
        Gregory Price <gregory.price@...verge.com>
Subject: Re: [PATCH V16 3/6] PCI/DOE: Add DOE mailbox support functions

On Tue, 19 Jul 2022 13:52:46 -0700
ira.weiny@...el.com wrote:

> From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> 
> Introduced in a PCIe r6.0, sec 6.30, DOE provides a config space based
> mailbox with standard protocol discovery.  Each mailbox is accessed
> through a DOE Extended Capability.
> 
> Each DOE mailbox must support the DOE discovery protocol in addition to
> any number of additional protocols.
> 
> Define core PCIe functionality to manage a single PCIe DOE mailbox at a
> defined config space offset.  Functionality includes iterating,
> creating, query of supported protocol, and task submission.  Destruction
> of the mailboxes is device managed.
> 
> Cc: "Li, Ming" <ming4.li@...el.com>
> Cc: Bjorn Helgaas <helgaas@...nel.org>
> Cc: Matthew Wilcox <willy@...radead.org>
> Acked-by: Bjorn Helgaas <helgaas@...nel.org>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> Co-developed-by: Ira Weiny <ira.weiny@...el.com>
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>

FYI. Gregory Price reported an an issue that I think
is related to calling INIT_WORK() rather than INIT_WORK_ONSTACK()
and associated debug options in his build.

https://lore.kernel.org/linux-cxl/20221014151045.24781-1-Jonathan.Cameron@huawei.com/T/#m88a7f50dcce52f30c8bf5c3dcc06fa9843b54a2d

I've highlighted one path to this below.

> diff --git a/drivers/pci/doe.c b/drivers/pci/doe.c
> new file mode 100644
> index 000000000000..e402f05068a5
> --- /dev/null
> +++ b/drivers/pci/doe.c
> @@ -0,0 +1,536 @@


> +static int pci_doe_discovery(struct pci_doe_mb *doe_mb, u8 *index, u16 *vid,
> +			     u8 *protocol)
> +{
> +	u32 request_pl = FIELD_PREP(PCI_DOE_DATA_OBJECT_DISC_REQ_3_INDEX,
> +				    *index);
> +	u32 response_pl;
> +	DECLARE_COMPLETION_ONSTACK(c);
> +	struct pci_doe_task task = {
> +		.prot.vid = PCI_VENDOR_ID_PCI_SIG,
> +		.prot.type = PCI_DOE_PROTOCOL_DISCOVERY,
> +		.request_pl = &request_pl,
> +		.request_pl_sz = sizeof(request_pl),
> +		.response_pl = &response_pl,
> +		.response_pl_sz = sizeof(response_pl),
> +		.complete = pci_doe_task_complete,
> +		.private = &c,
> +	};
This structure contains a work_struct and is on the stack.  However...

> +	int rc;
> +
> +	rc = pci_doe_submit_task(doe_mb, &task);
> +	if (rc < 0)
> +		return rc;
> +
> +	wait_for_completion(&c);
> +
> +	if (task.rv != sizeof(response_pl))
> +		return -EIO;
> +
> +	*vid = FIELD_GET(PCI_DOE_DATA_OBJECT_DISC_RSP_3_VID, response_pl);
> +	*protocol = FIELD_GET(PCI_DOE_DATA_OBJECT_DISC_RSP_3_PROTOCOL,
> +			      response_pl);
> +	*index = FIELD_GET(PCI_DOE_DATA_OBJECT_DISC_RSP_3_NEXT_INDEX,
> +			   response_pl);
> +
> +	return 0;
> +}

...

> +int pci_doe_submit_task(struct pci_doe_mb *doe_mb, struct pci_doe_task *task)
> +{
> +	if (!pci_doe_supports_prot(doe_mb, task->prot.vid, task->prot.type))
> +		return -EINVAL;
> +
> +	/*
> +	 * DOE requests must be a whole number of DW and the response needs to
> +	 * be big enough for at least 1 DW
> +	 */
> +	if (task->request_pl_sz % sizeof(u32) ||
> +	    task->response_pl_sz < sizeof(u32))
> +		return -EINVAL;
> +
> +	if (test_bit(PCI_DOE_FLAG_DEAD, &doe_mb->flags))
> +		return -EIO;
> +
> +	task->doe_mb = doe_mb;
> +	INIT_WORK(&task->work, doe_statemachine_work);

Here we don't call the INIT_WORK_ONSTACK() Variant.

> +	queue_work(doe_mb->work_queue, &task->work);
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(pci_doe_submit_task);