linux-kernel - Re: [PATCHv8 0/5] Driver for new "VMD" device

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Date:	Tue, 23 Feb 2016 18:24:00 +0000
From:	Keith Busch <keith.busch@...el.com>
To:	Bjorn Helgaas <helgaas@...nel.org>
Cc:	"Veal, Bryan E." <bryan.e.veal@...el.com>,
	LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
	linux-pci@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Jon Derrick <jonathan.derrick@...el.com>
Subject: Re: [PATCHv8 0/5] Driver for new "VMD" device

On Mon, Feb 22, 2016 at 04:10:24PM -0600, Bjorn Helgaas wrote:
> I'm not sure how to deal with the question of a hot-added VMD.  Maybe
> all we can do now is add a comment to the effect that we assume BIOS
> has assigned the non-prefetchable BAR below 4GB, and if Linux assigns
> that BAR for hot-added VMDs, that assumption will likely break.

Yes, we can assume BIOS always assigns. There are other BIOS dependencies
in order for the host to see the h/w as a VMD endpoint.

> diff --git a/arch/x86/pci/vmd.c b/arch/x86/pci/vmd.c
> index d57e480..7554722 100644
> --- a/arch/x86/pci/vmd.c
> +++ b/arch/x86/pci/vmd.c
> @@ -532,6 +532,16 @@ static int vmd_enable_domain(struct vmd_dev *vmd)
>  		.flags = IORESOURCE_BUS | IORESOURCE_PCI_FIXED,
>  	};
>  
> +	/*
> +	 * If the window is below 4GB, clear IORESOURCE_MEM_64 so we can
> +	 * put 32-bit resources in the window.
> +	 *
> +	 * There's no hardware reason why a 64-bit window *couldn't*
> +	 * contain a 32-bit resource, but pbus_size_mem() computes the
> +	 * bridge window size assuming a 64-bit window will contain no
> +	 * 32-bit resources.  __pci_assign_resource() enforces that
> +	 * artificial restriction to make sure everything will fit.
> +	 */

This sounds good to me. Thanks!

>  	res = &vmd->dev->resource[VMD_MEMBAR1];
>  	upper_bits = upper_32_bits(res->end);
>  	flags = res->flags & ~IORESOURCE_SIZEALIGN;