Date: Thu, 24 Jan 2008 19:47:55 -0800
From: Yinghai Lu <Yinghai.Lu@Sun.COM>
Subject: [PATCH] x86: trim ram need to check if mtrr is there v2
In-reply-to: <4799400C.1060102@zytor.com>
To: "H. Peter Anvin" <hpa@zytor.com>, Jeremy Fitzhardinge <jeremy@goop.org>,
       Ingo Molnar <mingo@elte.hu>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Message-id: <200801241947.55223.yinghai.lu@sun.com>
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[PATCH] x86: trim ram need to check if mtrr is there v2

> >Jeremy Fitzhardinge wrote:
> > When booting a current x86.git kernel under kvm, I get this:
> > 
> > (qemu) Linux version 2.6.24-rc8 (jeremy@ezr) (gcc version 4.1.2 20070925 
> > (Red Hat 4.1.2-33)) #1928 SMP PREEMPT Thu Jan 24 17:09:04 PST 2008
> > early_ioremap_init()
> > BIOS-provided physical RAM map:
> > BIOS-e820: 0000000000000000 - 000000000009fc00 (usable)
> > BIOS-e820: 000000000009fc00 - 00000000000a0000 (reserved)
> > BIOS-e820: 00000000000e8000 - 0000000000100000 (reserved)
> > BIOS-e820: 0000000000100000 - 000000001fff0000 (usable)
> > BIOS-e820: 000000001fff0000 - 0000000020000000 (ACPI data)
> > BIOS-e820: 00000000fffc0000 - 0000000100000000 (reserved)
> > console [earlyser0] enabled
> > 0MB HIGHMEM available.
> > 511MB LOWMEM available.
> > Scan SMP from c0000000 for 1024 bytes.
> > Scan SMP from c009fc00 for 1024 bytes.
> > Scan SMP from c00f0000 for 65536 bytes.
> > Scan SMP from c009fc00 for 1024 bytes.
> > ***************
> > **** WARNING: likely BIOS bug
> > **** MTRRs don't cover all of memory, trimmed 131056 pages
> > ***************
> 
> H. Peter Anvin wrote:
> Looks like the code doesn't check that the CPU *has* MTRRs...

so check it mtrr is there, also check if mem less 4G and is AMD as early

Signed-off-by: Yinghai Lu <yinghai.lu@sun.com>

Index: linux-2.6/arch/x86/kernel/cpu/mtrr/main.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/cpu/mtrr/main.c
+++ linux-2.6/arch/x86/kernel/cpu/mtrr/main.c
@@ -642,13 +642,10 @@ early_param("disable_mtrr_trim", disable
 #define Tom2Enabled (1U << 21)
 #define Tom2ForceMemTypeWB (1U << 22)
 
-static __init int amd_special_default_mtrr(unsigned long end_pfn)
+static __init int amd_special_default_mtrr(void)
 {
 	u32 l, h;
 
-	/* Doesn't apply to memory < 4GB */
-	if (end_pfn <= (0xffffffff >> PAGE_SHIFT))
-		return 0;
 	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD)
 		return 0;
 	if (boot_cpu_data.x86 < 0xf || boot_cpu_data.x86 > 0x11)
@@ -682,6 +679,13 @@ int __init mtrr_trim_uncached_memory(uns
 	mtrr_type type;
 	u64 trim_start, trim_size;
 
+	if (!cpu_has_mtrr)
+		return 0;
+
+	/* Doesn't apply to memory < 4GB */
+	if (end_pfn <= (0xffffffffUL >> PAGE_SHIFT))
+		return 0;
+
 	/*
 	 * Make sure we only trim uncachable memory on machines that
 	 * support the Intel MTRR architecture:
@@ -691,6 +695,9 @@ int __init mtrr_trim_uncached_memory(uns
 	if (!is_cpu(INTEL) || disable_mtrr_trim || def != MTRR_TYPE_UNCACHABLE)
 		return 0;
 
+	if (amd_special_default_mtrr())
+		return 0;
+
 	/* Find highest cached pfn */
 	for (i = 0; i < num_var_ranges; i++) {
 		mtrr_if->get(i, &base, &size, &type);
@@ -702,9 +709,6 @@ int __init mtrr_trim_uncached_memory(uns
 			highest_addr = base + size;
 	}
 
-	if (amd_special_default_mtrr(end_pfn))
-		return 0;
-
 	if ((highest_addr >> PAGE_SHIFT) < end_pfn) {
 		printk(KERN_WARNING "***************\n");
 		printk(KERN_WARNING "**** WARNING: likely BIOS bug\n");
--
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