linux-kernel - Re: [regression, bisected, pci/iommu] Bug 216865 - Black screen when amdgpu started during 6.2-rc1 boot with AMD IOMMU enabled

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Date:   Thu, 5 Jan 2023 16:16:20 +0530
From:   Vasant Hegde <vasant.hegde@....com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>,
        Matt Fagnani <matt.fagnani@...l.net>,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        Alex Deucher <alexander.deucher@....com>,
        Joerg Roedel <jroedel@...e.de>
Cc:     "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        LKML <linux-kernel@...r.kernel.org>,
        "regressions@...ts.linux.dev" <regressions@...ts.linux.dev>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [regression, bisected, pci/iommu] Bug 216865 - Black screen when amdgpu started during 6.2-rc1 boot with AMD IOMMU enabled

Baolu,


On 1/5/2023 4:07 PM, Baolu Lu wrote:
> On 2023/1/5 18:27, Vasant Hegde wrote:
>> On 1/5/2023 6:39 AM, Matt Fagnani wrote:
>>> I built 6.2-rc2 with the patch applied. The same black screen problem happened
>>> with 6.2-rc2 with the patch. I tried to use early kdump with 6.2-rc2 with the
>>> patch twice by panicking the kernel with sysrq+alt+c after the black screen
>>> happened. The system rebooted after about 10-20 seconds both times, but no kdump
>>> and dmesg files were saved in /var/crash. I'm attaching the lspci -vvv output as
>>> requested.
>>>
>> Thanks for testing. As mentioned earlier I was not expecting this patch to fix
>> the black screen issue. It should fix kernel warnings and IOMMU page fault
>> related call traces. By any chance do you have the kernel boot logs?
>>
>>
>> @Baolu,
>>    Looking into lspci output, it doesn't list ACS feature for Graphics card. So
>> with your fix it didn't enable PASID and hence it failed to boot.
> 
> So do you mind telling why does the PASID need to be enabled for the
> graphic device? Or in another word, what does the graphic driver use the
> PASID for?

Honestly I don't know the complete details of how PASID works with graphics
card. May be Alex or Joerg can explain it better.

-Vasant