linux-kernel - Re: [tip:x86/urgent] x86/quirks: Add early quirk to reset Apple AirPort card

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Date:	Thu, 9 Jun 2016 09:37:53 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Lukas Wunner <lukas@...ner.de>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>, cmilsted@...hat.com,
	"Rafa?? Mi??ecki" <zajec5@...il.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Matthew Garrett <mjg59@...f.ucam.org>, m@...s.ch,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:x86/urgent] x86/quirks: Add early quirk to reset Apple
 AirPort card

On Thu, Jun 9, 2016 at 4:04 AM, Lukas Wunner <lukas@...ner.de> wrote:
> Subject: [PATCH] x86/quirks: Validate secondary bus number
>
> We used to brute-force scan buses 0 to 31 until commit 8659c406ade3
> ("x86: only scan the root bus in early PCI quirks") constrained the scan
> to the root bus, in part to shorten boot time.
>
> Commit 625a99d9bfd0 ("x86/quirks: Add early quirk to reset Apple AirPort
> card") reintroduced scanning of secondary buses, but used a recursive
> strategy to scan only buses that are actually present.
>
> However the secondary bus number read from a bridge's config space may
> be invalid, in particular a value of 0 causes an infinite loop. The PCI
> core goes beyond that and recurses to a child bus only if its bus number
> is greater than the parent bus number (see pci_scan_bridge()). Since the
> root bus is numbered 0, this implies that secondary buses may not be 0.
> Do the same on early scanning.
>
> Suggested-by: Yinghai Lu <yinghai@...nel.org>
> Fixes: 625a99d9bfd0 ("x86/quirks: Add early quirk to reset Apple AirPort card")
> Signed-off-by: Lukas Wunner <lukas@...ner.de>
> ---
>  arch/x86/kernel/early-quirks.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/early-quirks.c b/arch/x86/kernel/early-quirks.c
> index 4e4e499..c24070e 100644
> --- a/arch/x86/kernel/early-quirks.c
> +++ b/arch/x86/kernel/early-quirks.c
> @@ -747,7 +747,8 @@ static int __init check_dev_quirk(int num, int slot, int func)
>
>         if ((type & 0x7f) == PCI_HEADER_TYPE_BRIDGE) {
>                 sec = read_pci_config_byte(num, slot, func, PCI_SECONDARY_BUS);
> -               early_pci_scan_bus(sec);
> +               if (sec > num)
> +                       early_pci_scan_bus(sec);
>         }
>
>         if (!(type & 0x80))

If two bridges have sec, then early_pci_scan_bus still could be called
two times.

Maybe we can add one static array to recorded scanned bus.

static unsigned char scanned_bus[256];

and in early_pci_scan_bus check and set that before scanning.

Thanks

Yinghai