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

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Message-ID: <4fb1eb78-3746-752c-a38d-25783f674b26@gmail.com>
Date:   Thu, 19 Nov 2020 20:36:31 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Shay Agroskin <shayagr@...zon.com>
Cc:     kuba@...nel.org, netdev@...r.kernel.org, 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 19.11.2020 um 20:18 schrieb Shay Agroskin:
> 
> Heiner Kallweit <hkallweit1@...il.com> writes:
> 
>> 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));
> 
> Thank you for reviewing these patches. We will switch to using dma_set_...() instead
> 
>>>
>>
>> However instead of dev_err(&pdev->dev, ..) you could use pci_err(pdev, ..).
> 
> I see that pci_err evaluates to dev_err. While I see how using pci_* log function helps code readability, I prefer using
> dev_err here to keep the code consistent with the rest of the driver. We'll discuss changing all log functions in future patches to net-next if that's okay.
> 
The comment was just meant to make you aware of pci_err(), there's no need
to switch to it.