netdev - Re: [PATCH V1 net 2/4] net: ena: set initial DMA width to avoid intel iommu issue

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Date:   Wed, 18 Nov 2020 23:41:39 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Shay Agroskin <shayagr@...zon.com>, kuba@...nel.org,
        netdev@...r.kernel.org
Cc:     dwmw@...zon.com, zorik@...zon.com, matua@...zon.com,
        saeedb@...zon.com, msw@...zon.com, aliguori@...zon.com,
        nafea@...zon.com, gtzalik@...zon.com, netanel@...zon.com,
        alisaidi@...zon.com, benh@...zon.com, akiyano@...zon.com,
        sameehj@...zon.com, ndagan@...zon.com,
        Mike Cui <mikecui@...zon.com>
Subject: Re: [PATCH V1 net 2/4] net: ena: set initial DMA width to avoid intel
 iommu issue

Am 18.11.2020 um 23:35 schrieb Heiner Kallweit:
> Am 18.11.2020 um 22:59 schrieb Shay Agroskin:
>> The ENA driver uses the readless mechanism, which uses DMA, to find
>> out what the DMA mask is supposed to be.
>>
>> If DMA is used without setting the dma_mask first, it causes the
>> Intel IOMMU driver to think that ENA is a 32-bit device and therefore
>> disables IOMMU passthrough permanently.
>>
>> This patch sets the dma_mask to be ENA_MAX_PHYS_ADDR_SIZE_BITS=48
>> before readless initialization in
>> ena_device_init()->ena_com_mmio_reg_read_request_init(),
>> which is large enough to workaround the intel_iommu issue.
>>
>> DMA mask is set again to the correct value after it's received from the
>> device after readless is initialized.
>>
>> Fixes: 1738cd3ed342 ("net: ena: Add a driver for Amazon Elastic Network Adapters (ENA)")
>> Signed-off-by: Mike Cui <mikecui@...zon.com>
>> Signed-off-by: Arthur Kiyanovski <akiyano@...zon.com>
>> Signed-off-by: Shay Agroskin <shayagr@...zon.com>
>> ---
>>  drivers/net/ethernet/amazon/ena/ena_netdev.c | 13 +++++++++++++
>>  1 file changed, 13 insertions(+)
>>
>> diff --git a/drivers/net/ethernet/amazon/ena/ena_netdev.c b/drivers/net/ethernet/amazon/ena/ena_netdev.c
>> index 574c2b5ba21e..854a22e692bf 100644
>> --- a/drivers/net/ethernet/amazon/ena/ena_netdev.c
>> +++ b/drivers/net/ethernet/amazon/ena/ena_netdev.c
>> @@ -4146,6 +4146,19 @@ static int ena_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>>  		return rc;
>>  	}
>>  
>> +	rc = pci_set_dma_mask(pdev, DMA_BIT_MASK(ENA_MAX_PHYS_ADDR_SIZE_BITS));
>> +	if (rc) {
>> +		dev_err(&pdev->dev, "pci_set_dma_mask failed %d\n", rc);
>> +		goto err_disable_device;
>> +	}
>> +
>> +	rc = pci_set_consistent_dma_mask(pdev, DMA_BIT_MASK(ENA_MAX_PHYS_ADDR_SIZE_BITS));
>> +	if (rc) {
>> +		dev_err(&pdev->dev, "err_pci_set_consistent_dma_mask failed %d\n",
>> +			rc);
>> +		goto err_disable_device;
>> +	}
>> +
>>  	pci_set_master(pdev);
>>  
>>  	ena_dev = vzalloc(sizeof(*ena_dev));
>>
> 
> The old pci_ dma wrappers are being phased out and shouldn't be used in
> new code. See e.g. e059c6f340f6 ("tulip: switch from 'pci_' to 'dma_' API").
> So better use:
> dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(ENA_MAX_PHYS_ADDR_SIZE_BITS));
> 

However instead of dev_err(&pdev->dev, ..) you could use pci_err(pdev, ..).