linux-kernel - [PATCH][Regression] x86, 32-bit: trim memory not covered by wb mtrrs

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Message-Id: <200802071257.51893.balajirrao@gmail.com>
Date:	Thu, 7 Feb 2008 12:57:51 +0530
From:	Balaji Rao <balajirrao@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	jesse.barnes@...el.com, yhlu.kernel@...il.com, ak@...e.de,
	balajirrao@...il.com
Subject: [PATCH][Regression] x86, 32-bit: trim memory not covered by wb mtrrs - FIX

Hello,

The following commit caused my X server to stop working.

commit 99fc8d424bc5d803fe92cad56c068fe64e73747a
Author: Jesse Barnes <jesse.barnes@...el.com>
Date:   Wed Jan 30 13:33:18 2008 +0100

    x86, 32-bit: trim memory not covered by wb mtrrs

This patch fixes the improper handling of addresses > 4G by mtrr_trim_uncached_memory.
This, now brings up X on my system.

Signed-off-by: Balaji Rao <balajirrao@...il.com>

diff --git a/arch/x86/kernel/cpu/mtrr/main.c b/arch/x86/kernel/cpu/mtrr/main.c
index 1e27b69..b0f1d48 100644
--- a/arch/x86/kernel/cpu/mtrr/main.c
+++ b/arch/x86/kernel/cpu/mtrr/main.c
@@ -659,7 +659,7 @@ static __init int amd_special_default_mtrr(void)
  */
 int __init mtrr_trim_uncached_memory(unsigned long end_pfn)
 {
-	unsigned long i, base, size, highest_addr = 0, def, dummy;
+	unsigned long i, base, size, highest_pfn = 0, def, dummy;
 	mtrr_type type;
 	u64 trim_start, trim_size;
 
@@ -682,30 +682,27 @@ int __init mtrr_trim_uncached_memory(unsigned long end_pfn)
 		mtrr_if->get(i, &base, &size, &type);
 		if (type != MTRR_TYPE_WRBACK)
 			continue;
-		base <<= PAGE_SHIFT;
-		size <<= PAGE_SHIFT;
-		if (highest_addr < base + size)
-			highest_addr = base + size;
+		if (highest_pfn < base + size)
+			highest_pfn = base + size;
 	}
 
 	/* kvm/qemu doesn't have mtrr set right, don't trim them all */
-	if (!highest_addr) {
+	if (!highest_pfn) {
 		printk(KERN_WARNING "WARNING: strange, CPU MTRRs all blank?\n");
 		WARN_ON(1);
 		return 0;
 	}
 
-	if ((highest_addr >> PAGE_SHIFT) < end_pfn) {
+	if (highest_pfn < end_pfn) {
 		printk(KERN_WARNING "WARNING: BIOS bug: CPU MTRRs don't cover"
 			" all of memory, losing %LdMB of RAM.\n",
-			(((u64)end_pfn << PAGE_SHIFT) - highest_addr) >> 20);
+			((u64)(end_pfn - highest_pfn) << PAGE_SHIFT) >> 20);
 
 		WARN_ON(1);
 
 		printk(KERN_INFO "update e820 for mtrr\n");
-		trim_start = highest_addr;
-		trim_size = end_pfn;
-		trim_size <<= PAGE_SHIFT;
+		trim_start = highest_pfn << PAGE_SHIFT;
+		trim_size = end_pfn << PAGE_SHIFT;
 		trim_size -= trim_start;
 		add_memory_region(trim_start, trim_size, E820_RESERVED);
 		update_e820();
--
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