linux-kernel - Re: [PATCH 2/2] x86/PCI: limit the size of the 64bit window to 256GB v3

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Date:   Thu, 11 Jan 2018 08:21:41 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Christian König 
        <ckoenig.leichtzumerken@...il.com>
Cc:     bhelgaas@...gle.com, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, torvalds@...ux-foundation.org,
        aaro.koskinen@....fi, andy.shevchenko@...il.com,
        boris.ostrovsky@...cle.com, jgross@...e.com,
        alexander.deucher@....com, airlied@...ux.ie
Subject: Re: [PATCH 2/2] x86/PCI: limit the size of the 64bit window to 256GB
 v3

On Thu, Jan 11, 2018 at 02:23:30PM +0100, Christian König wrote:
> Avoid problems with BIOS implementations which don't report all used
> resources to the OS by only allocating a 256GB window directly below the
> hardware limit.
> 
> For the full hardware documentation see:
> https://support.amd.com/TechDocs/49125_15h_Models_30h-3Fh_BKDG.pdf

If you can supply a section number, I'll add it here.  That spec is 700
pages, so a hint would be useful.

> Fixes a silent reboot loop reported by Aaro Koskinen <aaro.koskinen@....fi> on
> an AMD-based MSI MS-7699/760GA-P43(FX) system.
> 
> v2: cleanup code a bit more, update comment and explain the hw limit
> v3: improve commit message
> 
> Link: https://lkml.kernel.org/r/20180105220412.fzpwqe4zljdawr36@darkstar.musicnaut.iki.fi
> Reported-by: Aaro Koskinen <aaro.koskinen@....fi>
> Signed-off-by: Christian König <christian.koenig@....com>
> ---
>  arch/x86/pci/fixup.c | 19 +++++++++----------
>  1 file changed, 9 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/pci/fixup.c b/arch/x86/pci/fixup.c
> index a91280da2ea1..9c1c98d7e3a7 100644
> --- a/arch/x86/pci/fixup.c
> +++ b/arch/x86/pci/fixup.c
> @@ -662,10 +662,11 @@ DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x2033, quirk_no_aersid);
>   */
>  static void pci_amd_enable_64bit_bar(struct pci_dev *dev)
>  {
> -	unsigned i;
>  	u32 base, limit, high;
> -	struct resource *res, *conflict;
>  	struct pci_dev *other;
> +	struct resource *res;
> +	unsigned i;
> +	int r;
>  
>  	if (!(pci_probe & PCI_BIG_ROOT_WINDOW))
>  		return;
> @@ -702,19 +703,17 @@ static void pci_amd_enable_64bit_bar(struct pci_dev *dev)
>  	if (!res)
>  		return;
>  
> +	/* Allocate a 256GB window directly below the 0xfd00000000 hw limit */
>  	res->name = "PCI Bus 0000:00";
>  	res->flags = IORESOURCE_PREFETCH | IORESOURCE_MEM |
>  		IORESOURCE_MEM_64 | IORESOURCE_WINDOW;
> -	res->start = 0x100000000ull;
> +	res->start = 0xbd00000000ull;
>  	res->end = 0xfd00000000ull - 1;
>  
> -	/* Just grab the free area behind system memory for this */
> -	while ((conflict = request_resource_conflict(&iomem_resource, res))) {
> -		if (conflict->end >= res->end) {
> -			kfree(res);
> -			return;
> -		}
> -		res->start = conflict->end + 1;
> +	r = request_resource(&iomem_resource, res);
> +	if (r) {
> +		kfree(res);
> +		return;
>  	}
>  
>  	dev_info(&dev->dev, "adding root bus resource %pR\n", res);
> -- 
> 2.11.0
>