linux-kernel - aperture_64.c: duplicated code, buggy?

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Date:	Mon, 26 May 2008 20:40:47 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	kernel list <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Dave Jones <davej@...emonkey.org.uk>,
	Andi Kleen <andi@...stfloor.org>
Subject: aperture_64.c: duplicated code, buggy?

Hi!

void __init early_gart_iommu_check(void)

contains

	for (num = 24; num < 32; num++) {
		if (!early_is_k8_nb(read_pci_config(0, num, 3, 0x00)))
			continue;

loop, with very similar loop duplicated in

void __init gart_iommu_hole_init(void)

. First copy of a loop seems to be buggy, too. It uses 0 as a "nothing
set" value, which may actually bite us in last_aper_enabled case
(because it may be often zero).

(Beware, it is hard to test this patch, because this code has about
2^8 different code paths, depending on hardware and cmdline settings).

Plus, the second loop does not check for consistency of
aper_enabled. Should it?

---

early_gart_iommu_check(void) uses 0 as a "nothing set" value, which
may actually bite us in last_aper_enabled case (because it may be
often zero).

Signed-off-by: Pavel Machek <pavel@...e.cz>

diff --git a/arch/x86/kernel/aperture_64.c b/arch/x86/kernel/aperture_64.c
index 4a3d8cf..2088b6a 100644
--- a/arch/x86/kernel/aperture_64.c
+++ b/arch/x86/kernel/aperture_64.c
@@ -241,11 +242,12 @@ void __init early_gart_iommu_check(void)
 	u32 ctl;
 	u32 aper_size = 0, aper_order = 0, last_aper_order = 0;
 	u64 aper_base = 0, last_aper_base = 0;
-	int aper_enabled = 0, last_aper_enabled = 0;
+	int aper_enabled = 0, last_aper_enabled = 0, last_valid = 0;
 
 	if (!early_pci_allowed())
 		return;
 
+	/* This is mostly duplicate of iommu_hole_init */
 	fix = 0;
 	for (num = 24; num < 32; num++) {
 		if (!early_is_k8_nb(read_pci_config(0, num, 3, 0x00)))
@@ -258,15 +260,17 @@ void __init early_gart_iommu_check(void)
 		aper_base = read_pci_config(0, num, 3, AMD64_GARTAPERTUREBASE) & 0x7fff;
 		aper_base <<= 25;
 
-		if ((last_aper_order && aper_order != last_aper_order) ||
-		    (last_aper_base && aper_base != last_aper_base) ||
-		    (last_aper_enabled && aper_enabled != last_aper_enabled)) {
-			fix = 1;
-			break;
-		}
+		if (last_valid)
+			if ((aper_order != last_aper_order) ||
+			    (aper_base != last_aper_base) ||
+			    (aper_enabled != last_aper_enabled)) {
+				fix = 1;
+				break;
+			}
 		last_aper_order = aper_order;
 		last_aper_base = aper_base;
 		last_aper_enabled = aper_enabled;
+		last_valid = 1;
 	}
 
 	if (!fix && !aper_enabled)


-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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