linux-kernel - Re: [RFC] iommu: Fix virtio-iommu probing

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Message-ID: <3fdbd23d-cd65-453b-aa8d-78f9ed1bc4c4@redhat.com>
Date: Thu, 14 Aug 2025 17:19:48 +0200
From: Eric Auger <eric.auger@...hat.com>
To: Robin Murphy <robin.murphy@....com>, eric.auger.pro@...il.com,
 rafael@...nel.org, bhelgaas@...gle.com, jgg@...pe.ca, lpieralisi@...nel.org,
 linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org, lenb@...nel.org,
 jean-philippe@...aro.org, jsnitsel@...hat.com
Subject: Re: [RFC] iommu: Fix virtio-iommu probing

Hi Robin

On 8/14/25 4:53 PM, Robin Murphy wrote:
> On 14/08/2025 3:17 pm, Eric Auger wrote:
>> Commit bcb81ac6ae3c ("iommu: Get DT/ACPI parsing into the proper
>> probe path") broke virtio-iommu probing and no iommu group are
>> produced anymore.
>>
>> When probe_iommu_group() gets called viommu_probe_device() fails
>> because viommu_get_by_fwnode(fwspec->iommu_fwnode) returns NULL.
>
> ...which it's not supposed to. And *now* I remember, we never got this
> finished, did we?
Seems we did not ;-)
>
> https://lore.kernel.org/linux-iommu/9beaed48da83a0882dba153e65e6cfd0a8e21482.1742484773.git.robin.murphy@arm.com/
>

Unfortunately it does not fix my issue. Still no iommu group when
booting with ACPI.

Thanks

Eric
>
> Thanks,
> Robin.
>
>> So it seems we need to restore the original iommu_probe_device
>> call site in acpi_iommu_configure_id() to get a chance to probe
>> the device again.
>>
>> Maybe this defeats the whole purpose of the original commit but
>> at least it fixes the virtio-iommu probing.
>>
>> Fixes: bcb81ac6ae3c ("iommu: Get DT/ACPI parsing into the proper
>> probe path")
>> Cc: stable@...r.kernel.org # v6.15+
>> Signed-off-by: Eric Auger <eric.auger@...hat.com>
>>
>> ---
>>
>> I also tested smmu probing and this seems to work fine.
>> ---
>>   drivers/acpi/scan.c | 7 +++++++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
>> index fb1fe9f3b1a3..9f4efa8f75a6 100644
>> --- a/drivers/acpi/scan.c
>> +++ b/drivers/acpi/scan.c
>> @@ -1632,6 +1632,13 @@ static int acpi_iommu_configure_id(struct
>> device *dev, const u32 *id_in)
>>           err = viot_iommu_configure(dev);
>>       mutex_unlock(&iommu_probe_device_lock);
>>   +    /*
>> +     * If we have reason to believe the IOMMU driver missed the initial
>> +     * iommu_probe_device() call for dev, replay it to get things in
>> order.
>> +     */
>> +    if (!err && dev->bus)
>> +        err = iommu_probe_device(dev);
>> +
>>       return err;
>>   }
>>   
>