Re: [PATCH V7 9/9] PCI/P2PDMA: Add a 10-Bit Tag check in P2PDMA

[Dongdong Liu <liudongdong3@huawei.com>]

Hi Logan

Many thanks for your review.
On 2021/8/4 23:56, Logan Gunthorpe wrote:
>
>
> On 2021-08-04 7:47 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. "echo 0 > /sys/bus/pci/devices/.../10bit_tag" to
>> disable 10-BIT Tag Requester for PF device.
>> "echo 0 > /sys/bus/pci/devices/.../sriov_vf_10bit_tag_ctl" to disable
>> 10-BIT Tag Requester for VF device.
>>
>> Signed-off-by: Dongdong Liu <liudongdong3@huawei.com>
>> ---
>>  drivers/pci/p2pdma.c | 40 ++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 40 insertions(+)
>>
>> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
>> index 50cdde3..948f2be 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,
>> @@ -410,6 +411,41 @@ static unsigned long map_types_idx(struct pci_dev *client)
>>  		(client->bus->number << 8) | client->devfn;
>>  }
>>
>> +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)) {
>
> I think the brackets around !comp are unnecessary.
Yes, will fix.
>
>> +		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));
>> +			if (a->is_virtfn)
>> +				pci_warn(a, "to disable 10-Bit Tag Requester for this device, echo 0 > /sys/bus/pci/devices/%s/sriov_vf_10bit_tag_ctl\n",
>> +					 pci_name(a));
>> +			else
>> +				pci_warn(a, "to disable 10-Bit Tag Requester for this device, echo 0 > /sys/bus/pci/devices/%s/10bit_tag\n",
>> +					 pci_name(a));
>
> Can we not simplify this slightly by having a const char * set to the
> tag in the above if (a->is_virtfn)?
>
> pci_warn(a, "to disable 10-Bit Tag Requester for this device, echo 0 >
> /sys/bus/pci/devices/%s/%s\n", pci_name(a), tag);
Good point, will fix.

Thanks,
Dongdong
>
>> +		}
>> +		return false;
>> +	}
>> +
>> +	return true;
>> +}
>> +
>>  /*
>>   * Calculate the P2PDMA mapping type and distance between two PCI devices.
>>   *
>> @@ -532,6 +568,10 @@ calc_map_type_and_dist(struct pci_dev *provider, struct pci_dev *client,
>>  		map_type = PCI_P2PDMA_MAP_NOT_SUPPORTED;
>>  	}
>>  done:
>> +	if (!check_10bit_tags_vaild(client, provider, verbose) ||
>> +	    !check_10bit_tags_vaild(provider, client, verbose))
>> +		map_type = PCI_P2PDMA_MAP_NOT_SUPPORTED;
>> +
>>  	rcu_read_lock();
>>  	p2pdma = rcu_dereference(provider->p2pdma);
>>  	if (p2pdma)
>>
> .
>