Re: [PATCH v3] PCI: vmd: always enable host bridge hotplug support flags

[Paul M Stillwell Jr <paul.m.stillwell.jr@intel.com>]

On 5/2/2024 3:08 PM, Bjorn Helgaas wrote:
> On Mon, Apr 08, 2024 at 11:39:27AM -0700, Paul M Stillwell Jr wrote:
>> Commit 04b12ef163d1 ("PCI: vmd: Honor ACPI _OSC on PCIe features") added
>> code to copy the _OSC flags from the root bridge to the host bridge for each
>> vmd device because the AER bits were not being set correctly which was
>> causing an AER interrupt storm for certain NVMe devices.
>>
>> This works fine in bare metal environments, but causes problems when the
>> vmd driver is run in a hypervisor environment. In a hypervisor all the
>> _OSC bits are 0 despite what the underlying hardware indicates. This is
>> a problem for vmd users because if vmd is enabled the user *always*
>> wants hotplug support enabled. To solve this issue the vmd driver always
>> enables the hotplug bits in the host bridge structure for each vmd.
>>
>> Fixes: 04b12ef163d1 ("PCI: vmd: Honor ACPI _OSC on PCIe features")
>> Signed-off-by: Nirmal Patel <nirmal.patel@linux.intel.com>
>> Signed-off-by: Paul M Stillwell Jr <paul.m.stillwell.jr@intel.com>
>> ---
>>   drivers/pci/controller/vmd.c | 10 ++++++++--
>>   1 file changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
>> index 87b7856f375a..583b10bd5eb7 100644
>> --- a/drivers/pci/controller/vmd.c
>> +++ b/drivers/pci/controller/vmd.c
>> @@ -730,8 +730,14 @@ static int vmd_alloc_irqs(struct vmd_dev *vmd)
>>   static void vmd_copy_host_bridge_flags(struct pci_host_bridge *root_bridge,
>>   				       struct pci_host_bridge *vmd_bridge)
>>   {
>> -	vmd_bridge->native_pcie_hotplug = root_bridge->native_pcie_hotplug;
>> -	vmd_bridge->native_shpc_hotplug = root_bridge->native_shpc_hotplug;
>> +	/*
>> +	 * there is an issue when the vmd driver is running within a hypervisor
>> +	 * because all of the _OSC bits are 0 in that case. this disables
>> +	 * hotplug support, but users who enable VMD in their BIOS always want
>> +	 * hotplug suuport so always enable it.
>> +	 */
>> +	vmd_bridge->native_pcie_hotplug = 1;
>> +	vmd_bridge->native_shpc_hotplug = 1;
> 
> Deferred for now because I think we need to figure out how to set all
> these bits the same, or at least with a better algorithm than "here's
> what we want in this environment."
> 
> Extended discussion about this at
> https://lore.kernel.org/r/20240417201542.102-1-paul.m.stillwell.jr@intel.com
> 

That's ok by me. I thought where we left it was that if we could find a 
solution to the Correctable Errors from the original issue that maybe we 
could revert 04b12ef163d1.

I'm not sure I would know if a patch that fixes the Correctable Errors 
comes in... We have a test case we would like to test against that was 
pre 04b12ef163d1 (BIOS has AER disabled and we hotplug a disk which 
results in AER interrupts) so we would be curious if the issues we saw 
before goes away with a new patch for Correctable Errors.

Paul
>>   	vmd_bridge->native_aer = root_bridge->native_aer;
>>   	vmd_bridge->native_pme = root_bridge->native_pme;
>>   	vmd_bridge->native_ltr = root_bridge->native_ltr;
>> -- 
>> 2.39.1
>>
>