netdev - Re: [PATCH V6 8/8] PCI/P2PDMA: Add a 10-bit tag check in P2PDMA

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Message-ID: <24bc5deb-1fa3-8e81-2d9d-18836dc3aec9@deltatee.com>
Date:   Fri, 23 Jul 2021 10:25:51 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Dongdong Liu <liudongdong3@...wei.com>, helgaas@...nel.org,
        hch@...radead.org, kw@...ux.com, linux-pci@...r.kernel.org,
        rajur@...lsio.com, hverkuil-cisco@...all.nl
Cc:     linux-media@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH V6 8/8] PCI/P2PDMA: Add a 10-bit tag check in P2PDMA




On 2021-07-23 5:06 a.m., Dongdong Liu wrote:
> Add a 10-Bit Tag check in the P2PDMA code to ensure that a device with
> 10-Bit Tag Requester doesn't interact with a device that does not
> support 10-BIT tag Completer. Before that happens, the kernel should
> emit a warning saying to enable a ”pci=disable_10bit_tag=“ kernel
> parameter.
> 
> Signed-off-by: Dongdong Liu <liudongdong3@...wei.com>
> ---
>  drivers/pci/p2pdma.c | 38 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
> 
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 50cdde3..bd93840 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -19,6 +19,7 @@
>  #include <linux/random.h>
>  #include <linux/seq_buf.h>
>  #include <linux/xarray.h>
> +#include "pci.h"
>  
>  enum pci_p2pdma_map_type {
>  	PCI_P2PDMA_MAP_UNKNOWN = 0,
> @@ -541,6 +542,39 @@ calc_map_type_and_dist(struct pci_dev *provider, struct pci_dev *client,
>  	return map_type;
>  }
>  
> +
> +static bool check_10bit_tags_vaild(struct pci_dev *a, struct pci_dev *b,
> +				   bool verbose)
> +{
> +	bool req;
> +	bool comp;
> +	u16 ctl2;
> +
> +	if (a->is_virtfn) {
> +#ifdef CONFIG_PCI_IOV
> +		req = !!(a->physfn->sriov->ctrl &
> +			 PCI_SRIOV_CTRL_VF_10BIT_TAG_REQ_EN);
> +#endif
> +	} else {
> +		pcie_capability_read_word(a, PCI_EXP_DEVCTL2, &ctl2);
> +		req = !!(ctl2 & PCI_EXP_DEVCTL2_10BIT_TAG_REQ_EN);
> +	}
> +
> +	comp = !!(b->pcie_devcap2 & PCI_EXP_DEVCAP2_10BIT_TAG_COMP);
> +	if (req && (!comp)) {
> +		if (verbose) {
> +			pci_warn(a, "cannot be used for peer-to-peer DMA as 10-Bit Tag Requester enable is set in device (%s), but peer device (%s) does not support the 10-Bit Tag Completer\n",
> +				 pci_name(a), pci_name(b));
> +
> +			pci_warn(a, "to disable 10-Bit Tag Requester for this device, add the kernel parameter: pci=disable_10bit_tag=%s\n",
> +				 pci_name(a));
> +		}
> +		return false;
> +	}
> +
> +	return true;
> +}
> +
>  /**
>   * pci_p2pdma_distance_many - Determine the cumulative distance between
>   *	a p2pdma provider and the clients in use.
> @@ -579,6 +613,10 @@ int pci_p2pdma_distance_many(struct pci_dev *provider, struct device **clients,
>  			return -1;
>  		}
>  
> +		if (!check_10bit_tags_vaild(pci_client, provider, verbose) ||
> +		    !check_10bit_tags_vaild(provider, pci_client, verbose))
> +			not_supported = true;
> +

This check needs to be done in calc_map_type_and_dist(). The mapping
type needs to be correctly stored in the xarray cache as other functions
rely on the cached value (and upcoming work will be calling
calc_map_type_and_dist() without pci_p2pdma_distance_many()).

Logan