linux-kernel - Re: [PATCH 2/2] x86/PCI: limit the size of the 64bit window to 256GB v2

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Date:   Wed, 10 Jan 2018 12:02:30 -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,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Aaro Koskinen <aaro.koskinen@....fi>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Alex Deucher <alexander.deucher@....com>,
        David Airlie <airlied@...ux.ie>
Subject: Re: [PATCH 2/2] x86/PCI: limit the size of the 64bit window to 256GB
 v2

[+cc linux-pci, previous cc list]

On Wed, Jan 10, 2018 at 01:25:51PM +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.
> 
> v2: cleanup code a bit more, update comment and explain the hw limit

Fixes a silent reboot loop reported by Aaro Koskinen
<aaro.koskinen@....fi> on an AMD-based MSI MS-7699/760GA-P43(FX)
system.

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 */

Can you include a citation for the hardware limit in the changelog?
I'll try to dig it up myself if you don't beat me to it.

>  	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
>