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

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

On 2023/1/6 22:14, 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 ?)

Hi Matt,

Do you mind helping to test below change? No other change needed.

diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
index f9cc2e10b676..48f34cc996e4 100644
--- a/drivers/pci/ats.c
+++ b/drivers/pci/ats.c
@@ -382,8 +382,15 @@ int pci_enable_pasid(struct pci_dev *pdev, int 
features)
         if (!pasid)
                 return -EINVAL;

-       if (!pci_acs_path_enabled(pdev, NULL, PCI_ACS_RR | PCI_ACS_UF))
-               return -EINVAL;
+       if (pdev->multifunction) {
+               if (!pci_acs_path_enabled(pdev, NULL, PCI_ACS_RR | 
PCI_ACS_UF))
+                       return -EINVAL;
+       } else {
+               if (!pdev->bus->self ||
+                   !pci_acs_path_enabled(pdev->bus->self, NULL,
+                                         PCI_ACS_RR | PCI_ACS_UF))
+                       return -EINVAL;
+       }

         pci_read_config_word(pdev, pasid + PCI_PASID_CAP, &supported);
         supported &= PCI_PASID_CAP_EXEC | PCI_PASID_CAP_PRIV;

--
Best regards,
baolu