Re: [PROBLEM] c5.metal on AWS fails to kexec after "PCI: Explicitly put devices into D0 when initializing"

[Mario Limonciello <mario.limonciello@amd.com>]

On 12/4/2025 9:06 PM, Matthew Ruffell wrote:
> Hi Mario,
> 
> Again, thank you for your prompt response.
> 
>> That's at least what it seems like.  And I guess trying to set D0
>> without bus mastering enabling is causing a problem.
>>
>> Could you try adding a pci_set_master() call to pci_power_up()?  This is
>> what I have in mind (only compile tested):
>>
>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>> index b14dd064006c..68661e333032 100644
>> --- a/drivers/pci/pci.c
>> +++ b/drivers/pci/pci.c
>> @@ -1323,6 +1323,7 @@ int pci_power_up(struct pci_dev *dev)
>>                   return -EIO;
>>           }
>>
>> +       pci_set_master(dev);
>>           pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr);
>>           if (PCI_POSSIBLE_ERROR(pmcsr)) {
>>                   pci_err(dev, "Unable to change power state from %s to
>> D0, device inaccessible\n",
> 
> I built a test kernel, using the very same git hash as yesterday,
> 51ab33fc0a8bef9454849371ef897a1241911b37
> with this pci_set_master(dev) applied, and yes, kexec succeeds and the
> system boots normally.
> 
> Would you do a global pci_set_master(dev) like this, or would you gate
> it behind a check to see if the system is being kexec'd?

Well - the problem is kexec_in_progress() is only set on the way down.
You don't get any indication that you're booting /through/ kexec.

Furthermore as you point out elsewhere in this thread a crash that jumps 
into a crash kernel kdump doesn't ever set kexec_in_progress on the way 
down.

So considering that I /think/ this points at an assumption failure 
during bootup about bus mastering.

Bjorn,

How do you feel about calling pci_set_master() in the startup train 
somewhere?  In addition to Matthew's testing, I tried on a few systems 
of mine and it seems to work fine with calling pci_set_master() at that 
above specific location.  I checked with that on top of 6.18:

* Regular Reboot
* Kexec Reboot
* Shutdown / power up