Re: Question on context setup for passthrough

[Baolu Lu <baolu.lu@linux.intel.com>]

On 2025/2/22 2:26, Jerry Snitselaar wrote:
> On Fri, Feb 21, 2025 at 04:40:42PM +0800, Baolu Lu wrote:
>> On 2025/2/21 15:16, Jerry Snitselaar wrote:
>>> Hi Baolu,
>> Hi Jerry,
>>
>>> In context_setup_pass_through_cb there is a check that bails out
>>> if dev != &pdev->dev which doesn't exist in the code that sets up the
>>> context entries in the dma domain case. Is there a reason this check is
>>> done in the passthrough case?
>> The check "dev != &pdev->dev" was added to prevent setting a context for
>> a different device that has its own probe path.
> Hi Baolu,
> 
> Why is it different than what happens in the case with the callback in
> the dma domains case? Shouldn't pci_for_each_dma_alias already be
> deciding which devices get called with the callback?  This seems like
> it will always skip setting up the context entry for an alias when
> there is a pcie to pci bridge.

This appears to be a regression introduced by commit <2031c469f816>
('iommu/vt-d: Add support for static identity domain'). Previously, the
context setup for both identity and DMA domains was handled in a single
path, where the condition 'dev != &pdev->dev' did not cause an early
exit. This check was newly added by the commit.

> 
> My initial fix was just the dropping of the check in the callback,
> but I wasn't sure that was correct or not. So I decided to check
> with you, and go back and read some pci spec bits. 🙂

Can you please post a fix for this?

Thanks,
baolu