Impact: bugfix

Considering the situation as follow:

before: mcelog.next == 1, mcelog.entry[0].finished = 1

+--------------------------------------------------------------------------
R                   W1                  W2                  W3

read mcelog.next (1)
                    mcelog.next++ (2)
                    (working on entry 1,
                    finished == 0)

mcelog.next = 0
                                        mcelog.next++ (1)
                                        (working on entry 0)
                                                           mcelog.next++ (2)
                                                           (working on entry 1)
                        <----------------- race ---------------->
                    (done on entry 1,
                    finished = 1)
                                                           (done on entry 1,
                                                           finished = 1)

To fix the race condition, a cmpxchg loop is added to mce_read() to
ensure no new MCE record can be added between mcelog.next reading and
mcelog.next = 0.
Signed-off-by: NHuang Ying <ying.huang@intel.com>
Signed-off-by: NAndi Kleen <ak@linux.intel.com>
Acked-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Impact: Lower priority bug fix

Offlined CPUs could still get machine checks, but the machine check handler
cannot handle them properly, leading to an unconditional crash. Disable
machine checks on CPUs that are going down.
Signed-off-by: NAndi Kleen <ak@linux.intel.com>
Acked-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Impact: bug fix, in this case the resume handler shouldn't run which
	avoids incorrectly reenabling machine checks on resume

When MCEs are completely disabled on the command line don't set
up the sysdev devices for them either.

Includes a comment fix from Thomas Gleixner.
Signed-off-by: NAndi Kleen <ak@linux.intel.com>
Acked-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Impact: Higher priority bug fix

The machine check poller runs a single timer and then broadcasted an
IPI to all CPUs to check them. This leads to unnecessary
synchronization between CPUs. The original CPU running the timer has
to wait potentially a long time for all other CPUs answering. This is
also real time unfriendly and in general inefficient.

This was especially a problem on systems with a lot of events where
the poller run with a higher frequency after processing some events.
There could be more and more CPU time wasted with this, to
the point of significantly slowing down machines.

The machine check polling is actually fully independent per CPU, so
there's no reason to not just do this all with per CPU timers.  This
patch implements that.

Also switch the poller also to use standard timers instead of work
queues. It was using work queues to be able to execute a user program
on a event, but mce_notify_user() handles this case now with a
separate callback. So instead always run the poll code in in a
standard per CPU timer, which means that in the common case of not
having to execute a trigger there will be less overhead.

This allows to clean up the initialization significantly, because
standard timers are already up when machine checks get init'ed.  No
multiple initialization functions.

Thanks to Thomas Gleixner for some help.

Cc: thockin@google.com
v2: Use del_timer_sync() on cpu shutdown and don't try to handle
migrated timers.
v3: Add WARN_ON for timer running on unexpected CPU
Signed-off-by: NAndi Kleen <ak@linux.intel.com>
Acked-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Impact: Needed for bug fix in next patch

This relaxes the requirement that mce_notify_user has to run in process
context. Useful for future changes, but also leads to cleaner
behaviour now. Now instead mce_notify_user can be called directly
from interrupt (but not NMI) context.

The work queue only uses a single global work struct, which can be done safely
because it is always free to reuse before the trigger function is executed.
This way no events can be lost.
Signed-off-by: NAndi Kleen <ak@linux.intel.com>
Acked-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Impact: low priority bug fix

This removes part of a a patch I added myself some time ago. After some
consideration the patch was a bad idea. In particular it stopped machine check
exceptions during code patching.

To quote the comment:

        * MCEs only happen when something got corrupted and in this
        * case we must do something about the corruption.
        * Ignoring it is worse than a unlikely patching race.
        * Also machine checks tend to be broadcast and if one CPU
        * goes into machine check the others follow quickly, so we don't
        * expect a machine check to cause undue problems during to code
        * patching.

So undo the machine check related parts of
8f4e956b NMIs are still disabled.

This only removes code, the only additions are a new comment.
Signed-off-by: NAndi Kleen <ak@linux.intel.com>
Acked-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Impact: Bug fix

During suspend it is not reliable to process machine check
exceptions, because CPUs disappear but can still get machine check
broadcasts.  Also the system is slightly more likely to
machine check them, but the handler is typically not a position
to handle them in a meaningfull way.

So disable them during suspend and enable them during resume.

Also make sure they are always disabled on hot-unplugged CPUs.

This new code assumes that suspend always hotunplugs all
non BP CPUs.

v2: Remove the WARN_ONs Thomas objected to.
Signed-off-by: NAndi Kleen <ak@linux.intel.com>
Acked-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Impact: Bugfix

The ifdef for the apic clear on shutdown for the 64bit intel thermal
vector was incorrect and never triggered. Fix that.
Signed-off-by: NAndi Kleen <ak@linux.intel.com>
Acked-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Impact: bug fix (with tolerant == 3)

do_exit cannot be called directly from the exception handler because
it can sleep and the exception handler runs on the exception stack.
Use force_sig() instead.

Based on a earlier patch by Ying Huang who debugged the problem.
Signed-off-by: NAndi Kleen <ak@linux.intel.com>
Acked-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Impact: Bug fix

This fixes a long standing bug in the machine check code. On resume the
boot CPU wouldn't get its vendor specific state like thermal handling
reinitialized. This means the boot cpu wouldn't ever get any thermal
events reported again.

Call the respective initialization functions on resume

v2: Remove ancient init because they don't have a resume device anyways.
    Pointed out by Thomas Gleixner.
v3: Now fix the Subject too to reflect v2 change
Signed-off-by: NAndi Kleen <ak@linux.intel.com>
Acked-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Damien Wyart reported high ksoftirqd CPU usage (20%) on an
otherwise idle system.

The function-graph trace Damien provided:

>   799.521187 |   1)    <idle>-0    |               |  rcu_check_callbacks() {
>   799.521371 |   1)    <idle>-0    |               |  rcu_check_callbacks() {
>   799.521555 |   1)    <idle>-0    |               |  rcu_check_callbacks() {
>   799.521738 |   1)    <idle>-0    |               |  rcu_check_callbacks() {
>   799.521934 |   1)    <idle>-0    |               |  rcu_check_callbacks() {
>   799.522068 |   1)  ksoftir-2324  |               |                rcu_check_callbacks() {
>   799.522208 |   1)    <idle>-0    |               |  rcu_check_callbacks() {
>   799.522392 |   1)    <idle>-0    |               |  rcu_check_callbacks() {
>   799.522575 |   1)    <idle>-0    |               |  rcu_check_callbacks() {
>   799.522759 |   1)    <idle>-0    |               |  rcu_check_callbacks() {
>   799.522956 |   1)    <idle>-0    |               |  rcu_check_callbacks() {
>   799.523074 |   1)  ksoftir-2324  |               |                  rcu_check_callbacks() {
>   799.523214 |   1)    <idle>-0    |               |  rcu_check_callbacks() {
>   799.523397 |   1)    <idle>-0    |               |  rcu_check_callbacks() {
>   799.523579 |   1)    <idle>-0    |               |  rcu_check_callbacks() {
>   799.523762 |   1)    <idle>-0    |               |  rcu_check_callbacks() {
>   799.523960 |   1)    <idle>-0    |               |  rcu_check_callbacks() {
>   799.524079 |   1)  ksoftir-2324  |               |                  rcu_check_callbacks() {
>   799.524220 |   1)    <idle>-0    |               |  rcu_check_callbacks() {
>   799.524403 |   1)    <idle>-0    |               |  rcu_check_callbacks() {
>   799.524587 |   1)    <idle>-0    |               |  rcu_check_callbacks() {
>   799.524770 |   1)    <idle>-0    |               |  rcu_check_callbacks() {
> [ . . . ]

Shows rcu_check_callbacks() being invoked way too often. It should be called
once per jiffy, and here it is called no less than 22 times in about
3.5 milliseconds, meaning one call every 160 microseconds or so.

Why do we need to call rcu_pending() and rcu_check_callbacks() from the
idle loop of 32-bit x86, especially given that no other architecture does
this?

The following patch removes the call to rcu_pending() and
rcu_check_callbacks() from the x86 32-bit idle loop in order to
reduce the softirq load on idle systems.
Reported-by: NDamien Wyart <damien.wyart@free.fr>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Commit 3d2a71a5 ("x86, traps: converge
do_debug handlers") changed the preemption disable logic of do_debug()
so vm86_handle_trap() is called with preemption disabled resulting in:

 BUG: sleeping function called from invalid context at include/linux/kernel.h:155
 in_atomic(): 1, irqs_disabled(): 0, pid: 3005, name: dosemu.bin
 Pid: 3005, comm: dosemu.bin Tainted: G        W  2.6.29-rc1 #51
 Call Trace:
  [<c050d669>] copy_to_user+0x33/0x108
  [<c04181f4>] save_v86_state+0x65/0x149
  [<c0418531>] handle_vm86_trap+0x20/0x8f
  [<c064e345>] do_debug+0x15b/0x1a4
  [<c064df1f>] debug_stack_correct+0x27/0x2c
  [<c040365b>] sysenter_do_call+0x12/0x2f
 BUG: scheduling while atomic: dosemu.bin/3005/0x10000001

Restore the original calling convention and reenable preemption before
calling handle_vm86_trap().
Reported-by: NMichal Suchanek <hramrach@centrum.cz>
Cc: stable@kernel.org
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: fix "garbled display, laptop is unusable" bug

Commit e51a1ac2 ("x86, olpc: fix endian
bug in openfirmware workaround") breaks model comparison on OLPC; the value
0xc2 needs to be scaled up by olpc_board().

The pre-patch version was wrong, but accidentally worked anyway
(big-endian 0xc2 is big enough to satisfy all other board revisions,
but little endian 0xc2 is not).
Signed-off-by: NChris Ball <cjb@laptop.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Acked-by: NAndres Salomon <dilinger@queued.net>
Cc: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Between 2.6.23 and 2.6.24-rc1 a change was made that broke IBM LS21
systems that had the HPET enabled in the BIOS, resulting in boot hangs
for x86_64.

Specifically commit b8ce3359, which
merges the i386 and x86_64 HPET code.

Prior to this commit, when we setup the HPET timers in x86_64, we did
the following:

	hpet_writel(HPET_TN_ENABLE | HPET_TN_PERIODIC | HPET_TN_SETVAL |
                    HPET_TN_32BIT, HPET_T0_CFG);

However after the i386/x86_64 HPET merge, we do the following:

	cfg = hpet_readl(HPET_Tn_CFG(timer));
	cfg |= HPET_TN_ENABLE | HPET_TN_PERIODIC |
			HPET_TN_SETVAL | HPET_TN_32BIT;
	hpet_writel(cfg, HPET_Tn_CFG(timer));

However on LS21s with HPET enabled in the BIOS, the HPET_T0_CFG register
boots with Level triggered interrupts (HPET_TN_LEVEL) enabled. This
causes the periodic interrupt to be not so periodic, and that results in
the boot time hang I reported earlier in the delay calibration.

My fix: Always disable HPET_TN_LEVEL when setting up periodic mode.
Signed-off-by: NJohn Stultz <johnstul@us.ibm.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: Catch cases where lazy MMU state is active in a preemtible context

arch_flush_lazy_mmu_cpu() has been changed to disable preemption so
the checks in enter/leave will never trigger. Put the preemtible()
check into arch_flush_lazy_mmu_cpu() to catch such cases.
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

Impact: avoid access to percpu vars in preempible context

They are intended to be used whenever there's the possibility
that there's some stale state which is going to be overwritten
with a queued update, or to force a state change when we may be
in lazy mode.  Either way, we could end up calling it with
preemption enabled, so wrap the functions in their own little
preempt-disable section so they can be safely called in any
context (though preemption should never be enabled if we're actually
in a lazy state).

(Move out of line to avoid #include dependencies.)
Signed-off-by: NJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

Ptrace_detach() races with __ptrace_unlink() if the traced task is
reaped while detaching. This might cause a double-free of the BTS
buffer.

Change the ptrace_detach() path to only do the memory accounting in
ptrace_bts_detach() and leave the buffer free to ptrace_bts_untrace()
which will be called from __ptrace_unlink().

The fix follows a proposal from Oleg Nesterov.
Reported-by: NOleg Nesterov <oleg@redhat.com>
Signed-off-by: NMarkus Metzger <markus.t.metzger@intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

In i8237A_resume(), when resetting the DMA controller, the parameters to
dma_outb() were mixed up.
Signed-off-by: NClemens Ladisch <clemens@ladisch.de>
[ cleaned up the file a tiny bit. ]
Signed-off-by: NIngo Molnar <mingo@elte.hu>

do_device_not_available() is the handler for #NM and it declares that
it takes a unsigned long and calls math_emu(), which takes a long
argument and surprisingly expects the stack frame starting at the zero
argument would match struct math_emu_info, which isn't true regardless
of configuration in the current code.

This patch makes do_device_not_available() take struct pt_regs like
other exception handlers and initialize struct math_emu_info with
pointer to it and pass pointer to the math_emu_info to math_emulate()
like normal C functions do.  This way, unless gcc makes a copy of
struct pt_regs in do_device_not_available(), the register frame is
correctly accessed regardless of kernel configuration or compiler
used.

This doesn't fix all math_emu problems but it at least gets it
somewhat working.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Commit 6194ba6f ("x86: don't special-case
pmd allocations as much") made changes to the way we handle pmd allocations,
and while doing that it dropped a call to  paravirt_release_pd on the
pgd page from the pgd_dtor code path.

As a result of this missing release, the hypervisor is now unaware of the
pgd page being freed, and as a result it ends up tracking this page as a
page table page.

After this the guest may start using the same page for other purposes, and
depending on what use the page is put to, it may result in various performance
and/or functional issues ( hangs, reboots).

Since this release is only required for VMI, I now release the pgd page from
the (vmi)_pgd_free hook.
Signed-off-by: NAlok N Kataria <akataria@vmware.com>
Acked-by: NJeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Cc: <stable@kernel.org>

Impact: find right nr_irqs_gsi on some systems.

One test-system has gap between gsi's:

[    0.000000] ACPI: IOAPIC (id[0x04] address[0xfec00000] gsi_base[0])
[    0.000000] IOAPIC[0]: apic_id 4, version 0, address 0xfec00000, GSI 0-23
[    0.000000] ACPI: IOAPIC (id[0x05] address[0xfeafd000] gsi_base[48])
[    0.000000] IOAPIC[1]: apic_id 5, version 0, address 0xfeafd000, GSI 48-54
[    0.000000] ACPI: IOAPIC (id[0x06] address[0xfeafc000] gsi_base[56])
[    0.000000] IOAPIC[2]: apic_id 6, version 0, address 0xfeafc000, GSI 56-62
...
[    0.000000] nr_irqs_gsi: 38

So nr_irqs_gsi is not right. some irq for MSI will overwrite with io_apic.

need to get that with acpi_probe_gsi when acpi io_apic is used
Signed-off-by: NYinghai Lu <yinghai@kernel.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

For Intel 7400 series CPUs, the recommendation is to use a clflush on the
monitored address just before monitor and mwait pair [1].

This clflush makes sure that there are no false wakeups from mwait when the
monitored address was recently written to.

[1] "MONITOR/MWAIT Recommendations for Intel Xeon Processor 7400 series"
    section in specification update document of 7400 series
    http://download.intel.com/design/xeon/specupdt/32033601.pdfSigned-off-by: NVenkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Fix user-visible grammo.
Signed-off-by: NAlex Chiang <achiang@hp.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

This patch echoes what we already do on 32-bit since
90f7d25c, and prints the DMI
product name in show_regs, so that system specific problems can be
easily identified.
Signed-off-by: NKyle McMartin <kyle@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: fix to enable APIC for AMD Fam10h on chipsets with a missing/b0rked
	ACPI MP table (MADT)

Booting a 32bit kernel on an AMD Fam10h CPU running on chipsets with
missing/b0rked MP table leads to a hang pretty early in the boot process
due to the APIC not being initialized. Fix that by falling back to the
default APIC base address in 32bit code, as it is done in the 64bit
codepath.
Signed-off-by: NBorislav Petkov <borislav.petkov@amd.com>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Impact: Fixes dumpstack and KDB on 64 bits

This re-adds the old stack pointer to the top of the irqstack to help
with unwinding.  It was removed in commit d99015b1
as part of the save_args out-of-line work.

Both dumpstack and KDB require this information.
Signed-off-by: NMartin Hicks <mort@sgi.com>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Eric Paris reported:

> I have an hp dl785g5 which is unable to successfully run
> 2.6.29-0.66.rc3.fc11.x86_64 or 2.6.29-rc2-next-20090126.  During bootup
> (early in userspace daemons starting) I get the below BUG, which quickly
> renders the machine dead.  I assume it is because sparse_irq_lock never
> gets released when the BUG kills that task.

Adjust lock sequence when migrating a descriptor with
CONFIG_NUMA_MIGRATE_IRQ_DESC enabled.
Signed-off-by: NYinghai Lu <yinghai@kernel.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Signed-off-by: NDave Jones <davej@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

[
  mingo@elte.hu: these fixes are a subset of changes cherry-picked from:

     git://git.kernel.org:/pub/scm/linux/kernel/git/jejb/voyager-2.6.git

  They fix various problems that recent x86 changes caused in the Voyager
  subarchitecture: both APIC changes and cpumask changes and certain
  cleanups caused subarch assumptions to break.

  Most of these changes are obsolete as the subarch code has been removed
  from the x86 development tree - but we merge them upstream to make Voyager
  build and boot.
]
Signed-off-by: NJames Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Move DMA-mapping.txt to Documentation/PCI/.

DMA-mapping.txt was supposed to be moved from Documentation/ to
Documentation/PCI/.  The 00-INDEX files in those two directories
were updated, along with a few other text files, but the file
itself somehow escaped being moved, so move it and update more
text files and source files with its new location.
Signed-off-by: NRandy Dunlap <randy.dunlap@oracle.com>
Acked-by: NGreg Kroah-Hartman <gregkh@suse.de>
cc:	Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kerneloops.org is reporting a lot of these warnings that come due to
vmware not setting up any MTRRs for emulated CPUs:

| Reported 709 times (14696 total reports)
| BIOS bug (often in VMWare) where the MTRR's are set up incorrectly
| or not at all
|
| This warning was last seen in version 2.6.29-rc2-git1, and first
| seen in 2.6.24.
|
| More info:
|   http://www.kerneloops.org/searchweek.php?search=mtrr_trim_uncached_memory

Keep a one-liner KERN_INFO about it - so that we have so notice if empty
MTRRs are caused by native hardware/BIOS weirdness.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: re-enable CPUID unmasking on affected processors

As far as I am capable of discerning from the documentation,
MSR_IA32_MISC_ENABLE should be available for all family 0xf CPUs, as
well as family 6 for model >= 0xd (newer Pentium M).

The documentation on this isn't ideal, so we need to be on the lookout
for errors, still.
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Here function vmi_activate calls a init function activate_vmi , which
causes the following section mismatch warnings:

  LD      arch/x86/kernel/built-in.o
WARNING: arch/x86/kernel/built-in.o(.text+0x13ba9): Section mismatch
in reference from the function vmi_activate() to the function
.init.text:vmi_time_init()
The function vmi_activate() references
the function __init vmi_time_init().
This is often because vmi_activate lacks a __init
annotation or the annotation of vmi_time_init is wrong.

WARNING: arch/x86/kernel/built-in.o(.text+0x13bd1): Section mismatch
in reference from the function vmi_activate() to the function
.devinit.text:vmi_time_bsp_init()
The function vmi_activate() references
the function __devinit vmi_time_bsp_init().
This is often because vmi_activate lacks a __devinit
annotation or the annotation of vmi_time_bsp_init is wrong.

WARNING: arch/x86/kernel/built-in.o(.text+0x13bdb): Section mismatch
in reference from the function vmi_activate() to the function
.devinit.text:vmi_time_ap_init()
The function vmi_activate() references
the function __devinit vmi_time_ap_init().
This is often because vmi_activate lacks a __devinit
annotation or the annotation of vmi_time_ap_init is wrong.

Fix it by marking vmi_activate() as __init too.
Signed-off-by: NRakib Mullick <rakib.mullick@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: fix boot hang on pre-model-15 Intel CPUs

rdmsrl_safe() does not work in very early bootup code yet, because we
dont have the pagefault handler installed yet so exception section
does not get parsed. rdmsr_safe() will just crash and hang the bootup.

So limit the MSR_IA32_MISC_ENABLE MSR read to those CPU types that
support it.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Cleanup the cpuid check for DS configuration.

This also fixes a Corei7 CPUID enumeration bug.
Signed-off-by: NMarkus Metzger <markus.t.metzger@intel.com>
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: Fix debugobjects warning

debugobject enabled kernels spit out a warning in hpet code due to a
workqueue which is initialized on stack.

Add INIT_WORK_ON_STACK() which calls init_timer_on_stack() and use it
in hpet.
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

Impact: Fixes crashes with misconfigured BIOSes on XSAVE hardware

Avuton Olrich reported early boot crashes with v2.6.28 and
bisected it down to dc1e35c6
("x86, xsave: enable xsave/xrstor on cpus with xsave support").

If the CPUID limit bit in MSR_IA32_MISC_ENABLE is set, clear it to
make all CPUID information available.  This is required for some
features to work, in particular XSAVE.
Reported-and-bisected-by: NAvuton Olrich <avuton@gmail.com>
Tested-by: NAvuton Olrich <avuton@gmail.com>
Signed-off-by: NH. Peter Anvin <hpa@linux.intel.com>

while looking at:

  http://bugzilla.kernel.org/show_bug.cgi?id=11541

I realized that the mtrr.show param cannot work, because
the code is processed much too early.

This patch:
 - Declares mtrr.show as early_param
 - Stays consistent with the previous param (which I doubt
   that it ever worked), so mtrr.show=1 would still work
 - Declares mtrr_show as initdata
Signed-off-by: NThomas Renninger <trenn@suse.de>
Acked-by: NJan Beulich <jbeulich@novell.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

This reverts commit 4217458d.

Justin Madru bisected this commit, it was causing weird Firefox
crashes.

The reason is that GCC mis-optimizes (re-uses) the on-stack parameters of
the calling frame, which corrupts the syscall return pt_regs state and
thus corrupts user-space register state.

So we go back to the slightly less clean but more optimization-safe
method of getting to pt_regs. Also add a comment to explain this.

Resolves: http://bugzilla.kernel.org/show_bug.cgi?id=12505Reported-and-bisected-by: NJustin Madru <jdm64@gawab.com>
Tested-by: NJustin Madru <jdm64@gawab.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

-tip testing found this crash:

> [   35.258515] calling  acpi_cpufreq_init+0x0/0x127 @ 1
> [   35.264127] BUG: unable to handle kernel NULL pointer dereference at (null)
> [   35.267554] IP: [<ffffffff80478092>] __bitmap_intersects+0x48/0x73
> [   35.267554] PGD 0
> [   35.267554] Oops: 0000 [#1] SMP DEBUG_PAGEALLOC

arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c is still broken: there's no
allocation of the variable mask, so we pass in an uninitialized cmd.mask
field to drv_read(), which then passes it to the scheduler which then
crashes ...

Switch it over to the much simpler constant-cpumask-pointers approach.
Signed-off-by: NIngo Molnar <mingo@elte.hu>