Re: [PATCH v2 4/7] iommu: Let iommu.strict override ops->def_domain_type

Baolu Lu
2022-11-28T13:00:46Z

On 2022/11/28 19:10, Niklas Schnelle wrote:
> On Thu, 2022-11-17 at 09:55 +0800, Baolu Lu wrote:
>> On 2022/11/17 1:16, Niklas Schnelle wrote:
>>> When iommu.strict=1 is set or iommu_set_dma_strict() was called we
>>> should use IOMMU_DOMAIN_DMA irrespective of ops->def_domain_type.
>>>
>>> Signed-off-by: Niklas Schnelle<schnelle@linux.ibm.com>
>>> ---
>>> drivers/iommu/iommu.c | 3 +++
>>> 1 file changed, 3 insertions(+)
>>>
>>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>>> index 65a3b3d886dc..d9bf94d198df 100644
>>> --- a/drivers/iommu/iommu.c
>>> +++ b/drivers/iommu/iommu.c
>>> @@ -1562,6 +1562,9 @@ static int iommu_get_def_domain_type(struct device *dev)
>>> {
>>> const struct iommu_ops *ops = dev_iommu_ops(dev);
>>>
>>> + if (iommu_dma_strict)
>>> + return IOMMU_DOMAIN_DMA;
>> If any quirky device must work in IOMMU identity mapping mode, this
>> might introduce functional regression. At least for VT-d platforms, some
>> devices do require IOMMU identity mapping mode for functionality.
> That's a good point. How about instead of unconditionally returning
> IOMMU_DOMAIN_DMA we just do so if the domain type returned by ops-
>> def_domain_type uses a flush queue (i.e. the __IOMMU_DOMAIN_DMA_FQ bit
> is set). That way a device that only supports identity mapping gets to
> set that but iommu_dma_strict at least always prevents use of an IOVA
> flush queue.

def_domain_type returns IOMMU_DOMAIN_DMA, IOMMU_DOMAIN_IDENTIRY or 0
(don't care). From a code perspective, you can force IOMMU_DOMAIN_DMA if
def_domain_type() returns 0.

*But* you need to document the relationship between strict mode and
default domain type somewhere and get that agreed with Robin.

Best regards,
baolu