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

On some machines, buggy BIOSes don't properly setup WB MTRRs to cover all
available RAM, meaning the last few megs (or even gigs) of memory will be
marked uncached.  Since Linux tends to allocate from high memory addresses
first, this causes the machine to be unusably slow as soon as the kernel
starts really using memory (i.e.  right around init time).

This patch works around the problem by scanning the MTRRs at boot and
figuring out whether the current end_pfn value (setup by early e820 code)
goes beyond the highest WB MTRR range, and if so, trimming it to match.  A
fairly obnoxious KERN_WARNING is printed too, letting the user know that
not all of their memory is available due to a likely BIOS bug.

Something similar could be done on i386 if needed, but the boot ordering
would be slightly different, since the MTRR code on i386 depends on the
boot_cpu_data structure being setup.

This patch fixes a bug in the last patch that caused the code to run on
non-Intel machines (AMD machines apparently don't need it and it's untested
on other non-Intel machines, so best keep it off).

Further enhancements and fixes from:

  Yinghai Lu <Yinghai.Lu@Sun.COM>
  Andi Kleen <ak@suse.de>

Signed-off-by: Jesse Barnes <jesse.barnes@intel.com>
Tested-by: Justin Piszcz <jpiszcz@lucidpixels.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 116 insertions, 24 deletions

diff --git a/arch/x86/kernel/cpu/mtrr/main.c b/arch/x86/kernel/cpu/mtrr/main.c
index 60af5ed2b5c0..ccd36ed2187b 100644
--- a/arch/x86/kernel/cpu/mtrr/main.c
+++ b/arch/x86/kernel/cpu/mtrr/main.c
@@ -38,8 +38,8 @@
 #include <linux/cpu.h>
 #include <linux/mutex.h>
 
+#include <asm/e820.h>
 #include <asm/mtrr.h>
-
 #include <asm/uaccess.h>
 #include <asm/processor.h>
 #include <asm/msr.h>
@@ -47,7 +47,7 @@
 
 u32 num_var_ranges = 0;
 
-unsigned int *usage_table;
+unsigned int mtrr_usage_table[MAX_VAR_RANGES];
 static DEFINE_MUTEX(mtrr_mutex);
 
 u64 size_or_mask, size_and_mask;
@@ -121,13 +121,8 @@ static void __init init_table(void)
         int i, max;
 
         max = num_var_ranges;
-        if ((usage_table = kmalloc(max * sizeof *usage_table, GFP_KERNEL))
-            == NULL) {
-                printk(KERN_ERR "mtrr: could not allocate\n");
-                return;
-        }
         for (i = 0; i < max; i++)
-                usage_table[i] = 1;
+                mtrr_usage_table[i] = 1;
 }
 
 struct set_mtrr_data {
@@ -383,7 +378,7 @@ int mtrr_add_page(unsigned long base, unsigned long size,
                         goto out;
                 }
                 if (increment)
-                        ++usage_table[i];
+                        ++mtrr_usage_table[i];
                 error = i;
                 goto out;
         }
@@ -391,15 +386,15 @@ int mtrr_add_page(unsigned long base, unsigned long size,
         i = mtrr_if->get_free_region(base, size, replace);
         if (i >= 0) {
                 set_mtrr(i, base, size, type);
-                if (likely(replace < 0))
-                        usage_table[i] = 1;
-                else {
-                        usage_table[i] = usage_table[replace];
+                if (likely(replace < 0)) {
+                        mtrr_usage_table[i] = 1;
+                } else {
+                        mtrr_usage_table[i] = mtrr_usage_table[replace];
                         if (increment)
-                                usage_table[i]++;
+                                mtrr_usage_table[i]++;
                         if (unlikely(replace != i)) {
                                 set_mtrr(replace, 0, 0, 0);
-                                usage_table[replace] = 0;
+                                mtrr_usage_table[replace] = 0;
                         }
                 }
         } else
@@ -529,11 +524,11 @@ int mtrr_del_page(int reg, unsigned long base, unsigned long size)
                 printk(KERN_WARNING "mtrr: MTRR %d not used\n", reg);
                 goto out;
         }
-        if (usage_table[reg] < 1) {
+        if (mtrr_usage_table[reg] < 1) {
                 printk(KERN_WARNING "mtrr: reg: %d has count=0\n", reg);
                 goto out;
         }
-        if (--usage_table[reg] < 1)
+        if (--mtrr_usage_table[reg] < 1)
                 set_mtrr(reg, 0, 0, 0);
         error = reg;
  out:
@@ -593,16 +588,11 @@ struct mtrr_value {
         unsigned long   lsize;
 };
 
-static struct mtrr_value * mtrr_state;
+static struct mtrr_value mtrr_state[MAX_VAR_RANGES];
 
 static int mtrr_save(struct sys_device * sysdev, pm_message_t state)
 {
         int i;
-        int size = num_var_ranges * sizeof(struct mtrr_value);
-
-        mtrr_state = kzalloc(size,GFP_ATOMIC);
-        if (!mtrr_state)
-                return -ENOMEM;
 
         for (i = 0; i < num_var_ranges; i++) {
                 mtrr_if->get(i,
@@ -624,7 +614,6 @@ static int mtrr_restore(struct sys_device * sysdev)
                                  mtrr_state[i].lsize,
                                  mtrr_state[i].ltype);
         }
-        kfree(mtrr_state);
         return 0;
 }
 
@@ -635,6 +624,109 @@ 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)
+{
+        disable_mtrr_trim = 1;
+        return 0;
+}
+early_param("disable_mtrr_trim", disable_mtrr_trim_setup);
+
+/*
+ * Newer AMD K8s and later CPUs have a special magic MSR way to force WB
+ * for memory >4GB. Check for that here.
+ * Note this won't check if the MTRRs < 4GB where the magic bit doesn't
+ * apply to are wrong, but so far we don't know of any such case in the wild.
+ */
+#define Tom2Enabled (1U << 21)
+#define Tom2ForceMemTypeWB (1U << 22)
+
+static __init int amd_special_default_mtrr(unsigned long end_pfn)
+{
+        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)
+                return 0;
+        /* In case some hypervisor doesn't pass SYSCFG through */
+        if (rdmsr_safe(MSR_K8_SYSCFG, &l, &h) < 0)
+                return 0;
+        /*
+         * Memory between 4GB and top of mem is forced WB by this magic bit.
+         * Reserved before K8RevF, but should be zero there.
+         */
+        if ((l & (Tom2Enabled | Tom2ForceMemTypeWB)) ==
+                 (Tom2Enabled | Tom2ForceMemTypeWB))
+                return 1;
+        return 0;
+}
+
+/**
+ * mtrr_trim_uncached_memory - trim RAM not covered by MTRRs
+ *
+ * Some buggy BIOSes don't setup the MTRRs properly for systems with certain
+ * memory configurations.  This routine checks that the highest MTRR matches
+ * the end of memory, to make sure the MTRRs having a write back type cover
+ * all of the memory the kernel is intending to use. If not, it'll trim any
+ * memory off the end by adjusting end_pfn, removing it from the kernel's
+ * allocation pools, warning the user with an obnoxious message.
+ */
+int __init mtrr_trim_uncached_memory(unsigned long end_pfn)
+{
+        unsigned long i, base, size, highest_addr = 0, def, dummy;
+        mtrr_type type;
+        u64 trim_start, trim_size;
+
+        /*
+         * Make sure we only trim uncachable memory on machines that
+         * support the Intel MTRR architecture:
+         */
+        rdmsr(MTRRdefType_MSR, def, dummy);
+        def &= 0xff;
+        if (!is_cpu(INTEL) || disable_mtrr_trim || def != MTRR_TYPE_UNCACHABLE)
+                return 0;
+
+        /* Find highest cached pfn */
+        for (i = 0; i < num_var_ranges; i++) {
+                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 (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");
+                printk(KERN_WARNING "**** MTRRs don't cover all of "
+                       "memory, trimmed %ld pages\n", end_pfn -
+                       (highest_addr >> PAGE_SHIFT));
+                printk(KERN_WARNING "***************\n");
+
+                printk(KERN_INFO "update e820 for mtrr\n");
+                trim_start = highest_addr;
+                trim_size = end_pfn;
+                trim_size <<= PAGE_SHIFT;
+                trim_size -= trim_start;
+                add_memory_region(trim_start, trim_size, E820_RESERVED);
+                update_e820();
+                return 1;
+        }
+
+        return 0;
+}
+#endif
 
 /**
  * mtrr_bp_init - initialize mtrrs on the boot CPU