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

[Bjorn Helgaas <helgaas@kernel.org>]

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

>  	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
>