Re: [PATCH v4] PCI: vmd: Do not change the BIOS Hotplug setting on VMD rootports

[Lorenzo Pieralisi <lpieralisi@kernel.org>]

On Tue, Aug 29, 2023 at 01:10:22AM -0400, Nirmal Patel wrote:
> Currently during Host boot up, VMD UEFI driver loads and configures
> all the VMD endpoints devices and devices behind VMD. Then during
> VMD rootport creation, VMD driver honors ACPI settings for Hotplug,
> AER, DPC, PM and enables these features based on BIOS settings.
> 
> During the Guest boot up, ACPI settings along with VMD UEFI driver are
> not present in Guest BIOS which results in assigning default values to
> Hotplug, AER, DPC, etc. As a result hotplug is disabled on the VMD
> rootports in the Guest OS.
> 
> VMD driver in Guest should be able to see the same settings as seen
> by Host VMD driver. Because of the missing implementation of VMD UEFI
> driver in Guest BIOS, the Hotplug is disabled on VMD rootport in
> Guest OS. Hot inserted drives don't show up and hot removed drives
> do not disappear even if VMD supports Hotplug in Guest. This
> behavior is observed in various combinations of guest OSes i.e. RHEL,
> SLES and hypervisors i.e. KVM and ESXI.
> 
> This change will make the VMD Host and Guest Driver to keep the settings
> implemented by the UEFI VMD DXE driver and thus honoring the user
> selections for hotplug in the BIOS.
> 
> Signed-off-by: Nirmal Patel <nirmal.patel@linux.intel.com>
> ---
> v3->v4: Rewrite the commit log.
> v2->v3: Update the commit log.
> v1->v2: Update the commit log.
> ---
>  drivers/pci/controller/vmd.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> index 769eedeb8802..52c2461b4761 100644
> --- a/drivers/pci/controller/vmd.c
> +++ b/drivers/pci/controller/vmd.c
> @@ -701,8 +701,6 @@ 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;

How is the host bridge probed in the guest if there is no ACPI support ?

I would like to understand this better how this works.

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

I don't get why *only* the hotplug flag should not be copied. Either
you want to preserve them all or none.

I assume the issue is that in the host, the _OSC method is used to
probe for flags whereas in the guest you can't rely on it ?

Is there a use case where you *do* want to copy the flags from the
root_bridge to the vmd_bridge ?

This does not look solid to me.

Thanks,
Lorenzo