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Message-ID: <bb865b8f-6f8f-769a-6364-d46b45caca85@linux.intel.com>
Date: Sat, 7 Jan 2023 10:44:46 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Jason Gunthorpe <jgg@...dia.com>,
Vasant Hegde <vasant.hegde@....com>
Cc: Matt Fagnani <matt.fagnani@...l.net>,
Thorsten Leemhuis <regressions@...mhuis.info>,
Joerg Roedel <jroedel@...e.de>,
"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] BugĀ 216865 - Black screen when amdgpu started during 6.2-rc1 boot with AMD IOMMU enabled
On 1/6/2023 10:14 PM, Jason Gunthorpe wrote:
> On Thu, Jan 05, 2023 at 03:57:28PM +0530, Vasant Hegde wrote:
>> Matt,
>>
>> 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.
>
> The ACS checks being done are feature of the path not the end point or
> root port.
>
> If we are expecting ACS on the end port then it is just a bug in how
> the test was written.. The test should be a NOP because there are no
> switches in this topology.
>
> Looking at it, this seems to just be because pci_enable_pasid is
> calling pci_acs_path_enabled wrong, the only other user is here:
>
> for (bus = pdev->bus; !pci_is_root_bus(bus); bus = bus->parent) {
> if (!bus->self)
> continue;
>
> if (pci_acs_path_enabled(bus->self, NULL, REQ_ACS_FLAGS))
> break;
>
> pdev = bus->self;
>
> group = iommu_group_get(&pdev->dev);
> if (group)
> return group;
> }
>
> And notice it is calling it on pdev->bus not on pdev itself which
> naturally excludes the end point from the ACS validation.
>
> So try something like:
>
> if (!pci_acs_path_enabled(pdev->bus->self, NULL, PCI_ACS_RR | PCI_ACS_UF))
>
> (and probably need to check for null ?)
Yeah! This really is a misuse of pci_acs_path_enabled().
But if @pdev is an endpoint of a multiple function device, perhaps we
still need to check acs on it?
--
Best regards,
baolu
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