Re: [PATCH v3] PCI: vmd: Only assign OSC features in bare metal OS

[Nirmal Patel <nirmal.patel@linux.intel.com>]

On Mon, 13 Jul 2026 22:08:44 +0000
Nirmal Patel <nirmal.patel@intel.com> wrote:

> Copy valid OSC flags from root bridge only when OS can provide correct
> values. In virtual machine, all of the control features are disabled
> as hypervisor will not passthrough root bridge information to VM.
> 
> Signed-off-by: Nirmal Patel <nirmal.patel@linux.intel.com>
> Reviewed-by:  Andy Shevchenko <andriy.shevchenko@intel.com>
> ---
> v3 : Removed period from commit and added a black line.
> v2 : Added descriptive boolean and removed period from commit message.
> ---
> ---
>  drivers/pci/controller/vmd.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/pci/controller/vmd.c
> b/drivers/pci/controller/vmd.c index d4ae250d4bc6..7c7d110290d6 100644
> --- a/drivers/pci/controller/vmd.c
> +++ b/drivers/pci/controller/vmd.c
> @@ -782,6 +782,7 @@ static int vmd_enable_domain(struct vmd_dev *vmd,
> unsigned long features) resource_size_t membar2_offset = 0x2000;
>  	struct pci_bus *child;
>  	struct pci_dev *dev;
> +	bool vmd_in_guest;
>  	int ret;
>  
>  	/*
> @@ -862,14 +863,16 @@ static int vmd_enable_domain(struct vmd_dev
> *vmd, unsigned long features) .parent = res,
>  	};
>  
> +	/* Non-zero offset means guest/direct assign view. */
> +	vmd_in_guest = offset[0] || offset[1];
> +
>  	/*
>  	 * Currently MSI remapping must be enabled in guest
> passthrough mode
>  	 * due to some missing interrupt remapping plumbing. This is
> probably
>  	 * acceptable because the guest is usually CPU-limited and
> MSI
>  	 * remapping doesn't become a performance bottleneck.
>  	 */
> -	if (!(features & VMD_FEAT_CAN_BYPASS_MSI_REMAP) ||
> -	    offset[0] || offset[1]) {
> +	if (!(features & VMD_FEAT_CAN_BYPASS_MSI_REMAP) ||
> vmd_in_guest) { ret = vmd_alloc_irqs(vmd);
>  		if (ret)
>  			return ret;
> @@ -910,8 +913,10 @@ static int vmd_enable_domain(struct vmd_dev
> *vmd, unsigned long features) return -ENODEV;
>  	}
>  
> -
> vmd_copy_host_bridge_flags(pci_find_host_bridge(vmd->dev->bus),
> -
> to_pci_host_bridge(vmd->bus->bridge));
> +	/* Don't copy _OSC control flags in VM, it disables
> features. */
> +	if (!vmd_in_guest)
> +
> vmd_copy_host_bridge_flags(pci_find_host_bridge(vmd->dev->bus),
> +
> to_pci_host_bridge(vmd->bus->bridge)); 
>  	vmd_attach_resources(vmd);
>  	if (vmd->irq_domain)

Gentle reminder. 

Thanks
nirmal