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    SubjectRe: [PATCH] trim memory not covered by WB MTRRs
    Will see if it still patches against -rc4.

    On Thu, 7 Jun 2007, Jesse Barnes wrote:

    > 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 incorporates the feedback from Eric and Andi:
    > - use MAX_VAR_RANGES instead of NUM_VAR_RANGES
    > - move array declaration to header file as an extern
    > - add command line disable option "disable_mtrr_trim"
    > - don't run the trim code if the MTRR default type is cacheable
    > - don't run the trim code on non-Intel machines
    >
    > Justin, feel free to test again if you have time and add your
    > "Tested-by" signoff.
    >
    > Andi, as for large pages, do you think this is ok as is, or should
    > I trim a larger granularity? If so, what granularity?
    >
    > Signed-off-by: Jesse Barnes <jesse.barnes@intel.com>
    >
    > Thanks,
    > Jesse
    >
    > diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
    > index 5d0283c..cb728a8 100644
    > --- a/Documentation/kernel-parameters.txt
    > +++ b/Documentation/kernel-parameters.txt
    > @@ -553,6 +553,12 @@ and is between 256 and 4096 characters. It is defined in the file
    > See drivers/char/README.epca and
    > Documentation/digiepca.txt.
    >
    > + disable_mtrr_trim [X86-64]
    > + By default the kernel will trim any uncacheable
    > + memory out of your available memory pool based on
    > + MTRR settings. This parameter disables that behavior,
    > + possibly causing your machine to run very slowly.
    > +
    > dmascc= [HW,AX25,SERIAL] AX.25 Z80SCC driver with DMA
    > support available.
    > Format: <io_dev0>[,<io_dev1>[,..<io_dev32>]]
    > diff --git a/arch/i386/kernel/cpu/mtrr/generic.c b/arch/i386/kernel/cpu/mtrr/generic.c
    > index c4ebb51..8eb3085 100644
    > --- a/arch/i386/kernel/cpu/mtrr/generic.c
    > +++ b/arch/i386/kernel/cpu/mtrr/generic.c
    > @@ -13,7 +13,7 @@
    > #include "mtrr.h"
    >
    > struct mtrr_state {
    > - struct mtrr_var_range *var_ranges;
    > + struct mtrr_var_range var_ranges[MAX_VAR_RANGES];
    > mtrr_type fixed_ranges[NUM_FIXED_RANGES];
    > unsigned char enabled;
    > unsigned char have_fixed;
    > @@ -84,12 +84,6 @@ void get_mtrr_state(void)
    > struct mtrr_var_range *vrs;
    > unsigned lo, dummy;
    >
    > - if (!mtrr_state.var_ranges) {
    > - mtrr_state.var_ranges = kmalloc(num_var_ranges * sizeof (struct mtrr_var_range),
    > - GFP_KERNEL);
    > - if (!mtrr_state.var_ranges)
    > - return;
    > - }
    > vrs = mtrr_state.var_ranges;
    >
    > rdmsr(MTRRcap_MSR, lo, dummy);
    > diff --git a/arch/i386/kernel/cpu/mtrr/if.c b/arch/i386/kernel/cpu/mtrr/if.c
    > index c7d8f17..0e34a67 100644
    > --- a/arch/i386/kernel/cpu/mtrr/if.c
    > +++ b/arch/i386/kernel/cpu/mtrr/if.c
    > @@ -11,10 +11,6 @@
    > #include <asm/mtrr.h>
    > #include "mtrr.h"
    >
    > -/* RED-PEN: this is accessed without any locking */
    > -extern unsigned int *usage_table;
    > -
    > -
    > #define FILE_FCOUNT(f) (((struct seq_file *)((f)->private_data))->private)
    >
    > static const char *const mtrr_strings[MTRR_NUM_TYPES] =
    > diff --git a/arch/i386/kernel/cpu/mtrr/main.c b/arch/i386/kernel/cpu/mtrr/main.c
    > index 7202b98..ef552ba 100644
    > --- a/arch/i386/kernel/cpu/mtrr/main.c
    > +++ b/arch/i386/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 usage_table[MAX_VAR_RANGES];
    > static DEFINE_MUTEX(mtrr_mutex);
    >
    > u64 size_or_mask, size_and_mask;
    > @@ -121,11 +121,6 @@ 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;
    > }
    > @@ -589,16 +584,11 @@ 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,
    > @@ -620,7 +610,6 @@ static int mtrr_restore(struct sys_device * sysdev)
    > mtrr_state[i].lsize,
    > mtrr_state[i].ltype);
    > }
    > - kfree(mtrr_state);
    > return 0;
    > }
    >
    > @@ -631,6 +620,57 @@ static struct sysdev_driver mtrr_sysdev_driver = {
    > .resume = mtrr_restore,
    > };
    >
    > +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);
    > +
    > +/**
    > + * 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 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.
    > + */
    > +void __init mtrr_trim_uncached_memory(void)
    > +{
    > + unsigned long i, base, size, highest_addr = 0, def, dummy;
    > + mtrr_type type;
    > +
    > + /* Make sure we only trim uncachable memory on Intel machines */
    > + rdmsr(MTRRdefType_MSR, def, dummy);
    > + def &= 0xff;
    > + if (!use_intel() || disable_mtrr_trim || def != MTRR_TYPE_UNCACHABLE)
    > + return;
    > +
    > + /* 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 ((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");
    > + end_pfn = highest_addr >> PAGE_SHIFT;
    > + }
    > +}
    >
    > /**
    > * mtrr_bp_init - initialize mtrrs on the boot CPU
    > diff --git a/arch/i386/kernel/cpu/mtrr/mtrr.h b/arch/i386/kernel/cpu/mtrr/mtrr.h
    > index 289dfe6..627b339 100644
    > --- a/arch/i386/kernel/cpu/mtrr/mtrr.h
    > +++ b/arch/i386/kernel/cpu/mtrr/mtrr.h
    > @@ -14,6 +14,7 @@
    > #define MTRRphysMask_MSR(reg) (0x200 + 2 * (reg) + 1)
    >
    > #define NUM_FIXED_RANGES 88
    > +#define MAX_VAR_RANGES 256
    > #define MTRRfix64K_00000_MSR 0x250
    > #define MTRRfix16K_80000_MSR 0x258
    > #define MTRRfix16K_A0000_MSR 0x259
    > @@ -34,6 +35,8 @@
    > an 8 bit field: */
    > typedef u8 mtrr_type;
    >
    > +extern unsigned int usage_table[MAX_VAR_RANGES];
    > +
    > struct mtrr_ops {
    > u32 vendor;
    > u32 use_intel_if;
    > diff --git a/arch/x86_64/kernel/bugs.c b/arch/x86_64/kernel/bugs.c
    > index c3c6b91..c138eac 100644
    > --- a/arch/x86_64/kernel/bugs.c
    > +++ b/arch/x86_64/kernel/bugs.c
    > @@ -14,7 +14,6 @@
    > void __init check_bugs(void)
    > {
    > identify_cpu(&boot_cpu_data);
    > - mtrr_bp_init();
    > #if !defined(CONFIG_SMP)
    > printk("CPU: ");
    > print_cpu_info(&boot_cpu_data);
    > diff --git a/arch/x86_64/kernel/setup.c b/arch/x86_64/kernel/setup.c
    > index eb6524f..409b63c 100644
    > --- a/arch/x86_64/kernel/setup.c
    > +++ b/arch/x86_64/kernel/setup.c
    > @@ -266,6 +266,10 @@ void __init setup_arch(char **cmdline_p)
    > * we are rounding upwards:
    > */
    > end_pfn = e820_end_of_ram();
    > + /* Trim memory not covered by WB MTRRs */
    > + mtrr_bp_init();
    > + mtrr_trim_uncached_memory();
    > +
    > num_physpages = end_pfn;
    >
    > check_efer();
    > diff --git a/include/asm-x86_64/mtrr.h b/include/asm-x86_64/mtrr.h
    > index b557c48..cc62bd8 100644
    > --- a/include/asm-x86_64/mtrr.h
    > +++ b/include/asm-x86_64/mtrr.h
    > @@ -78,6 +78,7 @@ extern int mtrr_add_page (unsigned long base, unsigned long size,
    > unsigned int type, char increment);
    > extern int mtrr_del (int reg, unsigned long base, unsigned long size);
    > extern int mtrr_del_page (int reg, unsigned long base, unsigned long size);
    > +extern void mtrr_trim_uncached_memory(void);
    > # else
    > static __inline__ int mtrr_add (unsigned long base, unsigned long size,
    > unsigned int type, char increment)
    >
    -
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