x86_32: trim memory by updating e820

when MTRRs are not covering the whole e820 table, we need to trim the
RAM and need to update e820.

reuse some code on 64-bit as well.

here need to add early_get_cap and use it in early_cpu_detect, and move
mtrr_bp_init early.

The code successfully trimmed the memory map on Justin's system:

from:

 [    0.000000]  BIOS-e820: 0000000100000000 - 000000022c000000 (usable)

to:

 [    0.000000]   modified: 0000000100000000 - 0000000228000000 (usable)
 [    0.000000]   modified: 0000000228000000 - 000000022c000000 (reserved)

According to Justin it makes quite a difference:

|  When I boot the box without any trimming it acts like a 286 or 386,
|  takes about 10 minutes to boot (using raptor disks).

Signed-off-by: Yinghai Lu <yinghai.lu@sun.com>
Tested-by: Justin Piszcz <jpiszcz@lucidpixels.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 14 insertions, 8 deletions

diff --git a/arch/x86/kernel/cpu/mtrr/main.c b/arch/x86/kernel/cpu/mtrr/main.c
index ccd36ed2187b..ac4b6338f3f4 100644
--- a/arch/x86/kernel/cpu/mtrr/main.c
+++ b/arch/x86/kernel/cpu/mtrr/main.c
@@ -624,7 +624,6 @@ static struct sysdev_driver mtrr_sysdev_driver = {
         .resume         = mtrr_restore,
 };
 
-#ifdef CONFIG_X86_64
 static int disable_mtrr_trim;
 
 static int __init disable_mtrr_trim_setup(char *str)
@@ -643,13 +642,10 @@ early_param("disable_mtrr_trim", disable_mtrr_trim_setup);
 #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)
@@ -687,9 +683,14 @@ int __init mtrr_trim_uncached_memory(unsigned long end_pfn)
          * Make sure we only trim uncachable memory on machines that
          * support the Intel MTRR architecture:
          */
+        if (!is_cpu(INTEL) || disable_mtrr_trim)
+                return 0;
         rdmsr(MTRRdefType_MSR, def, dummy);
         def &= 0xff;
-        if (!is_cpu(INTEL) || disable_mtrr_trim || def != MTRR_TYPE_UNCACHABLE)
+        if (def != MTRR_TYPE_UNCACHABLE)
+                return 0;
+
+        if (amd_special_default_mtrr())
                 return 0;
 
         /* Find highest cached pfn */
@@ -703,8 +704,14 @@ int __init mtrr_trim_uncached_memory(unsigned long end_pfn)
                         highest_addr = base + size;
         }
 
-        if (amd_special_default_mtrr(end_pfn))
+        /* kvm/qemu doesn't have mtrr set right, don't trim them all */
+        if (!highest_addr) {
+                printk(KERN_WARNING "***************\n");
+                printk(KERN_WARNING "**** WARNING: likely strange cpu\n");
+                printk(KERN_WARNING "**** MTRRs all blank, cpu in qemu?\n");
+                printk(KERN_WARNING "***************\n");
                 return 0;
+        }
 
         if ((highest_addr >> PAGE_SHIFT) < end_pfn) {
                 printk(KERN_WARNING "***************\n");
@@ -726,7 +733,6 @@ int __init mtrr_trim_uncached_memory(unsigned long end_pfn)
 
         return 0;
 }
-#endif
 
 /**
  * mtrr_bp_init - initialize mtrrs on the boot CPU