linux-kernel - Re: [PATCH V3 2/2] cxl/doe: Request exclusive DOE access

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Message-ID: <20220927145836.0000572e@huawei.com>
Date:   Tue, 27 Sep 2022 14:58:36 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     <ira.weiny@...el.com>
CC:     Dan Williams <dan.j.williams@...el.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        "Ben Widawsky" <bwidawsk@...nel.org>, <linux-cxl@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>
Subject: Re: [PATCH V3 2/2] cxl/doe: Request exclusive DOE access

On Mon, 26 Sep 2022 14:57:11 -0700
ira.weiny@...el.com wrote:

> From: Ira Weiny <ira.weiny@...el.com>
> 
> The PCIE Data Object Exchange (DOE) mailbox is a protocol run over
> configuration cycles.  It assumes one initiator at a time.  While the
> kernel has control of the mailbox user space writes could interfere with
> the kernel access.
> 
> Mark DOE mailbox config space exclusive when iterated by the CXL driver.
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
I wonder a bit on whether the failure should be fatal given that something
very odd would be required for it to fail.

I'm not that bothered though.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>

> 
> ---
> Changes from V2:
> 	Jonathan:
> 		s/PCI_DOE_CAP_SIZE/PCI_DOE_CAP_SIZEOF
> 		Set PCI_DOE_CAP_SIZEOF directly
> ---
>  drivers/cxl/pci.c             | 5 +++++
>  include/uapi/linux/pci_regs.h | 1 +
>  2 files changed, 6 insertions(+)
> 
> diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
> index faeb5d9d7a7a..621a0522b554 100644
> --- a/drivers/cxl/pci.c
> +++ b/drivers/cxl/pci.c
> @@ -418,6 +418,11 @@ static void devm_cxl_pci_create_doe(struct cxl_dev_state *cxlds)
>  			continue;
>  		}
>  
> +		if (!pci_request_config_region_exclusive(pdev, off,
> +							 PCI_DOE_CAP_SIZEOF,
> +							 dev_name(dev)))
> +			pci_err(pdev, "Failed to exclude DOE registers\n");
> +
>  		if (xa_insert(&cxlds->doe_mbs, off, doe_mb, GFP_KERNEL)) {
>  			dev_err(dev, "xa_insert failed to insert MB @ %x\n",
>  				off);
> diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
> index 57b8e2ffb1dd..82a03ea954af 100644
> --- a/include/uapi/linux/pci_regs.h
> +++ b/include/uapi/linux/pci_regs.h
> @@ -1119,6 +1119,7 @@
>  #define  PCI_DOE_STATUS_DATA_OBJECT_READY	0x80000000  /* Data Object Ready */
>  #define PCI_DOE_WRITE		0x10    /* DOE Write Data Mailbox Register */
>  #define PCI_DOE_READ		0x14    /* DOE Read Data Mailbox Register */
> +#define PCI_DOE_CAP_SIZEOF	0x18	/* Size of DOE register block */
>  
>  /* DOE Data Object - note not actually registers */
>  #define PCI_DOE_DATA_OBJECT_HEADER_1_VID		0x0000ffff