[PATCH v3 0/2] Forcibly enable some MISC_ENABLE features on Intel

[PATCH v3 0/2] Forcibly enable some MISC_ENABLE features on Intel

[Andy Lutomirski]

Intel allows BIOS or the OS to enable or disable some CPU fueatures via
IA32_MISC_ENABLE.  I have machines that don't enable fast strings or
monitor/mwait in BIOS, so do it on bootup instead.

The Intel SDM volume 3, appendix B.1 says that the OS should not touch
the monitor enable bit if SSE3 is not present, which presumably means
that the OS may touch that bit if SSE3 is present.  In any case, these
patches seem to work.

Changes from v2:
 - Don't linebreak printk messages (for ease of grepping)
 - Use printk_once
 - Update the "Disabled fast string operations" message

Changes from v1:
 - Display FW_WARN messages.
 - Don't change the kmemcheck message.
 - Improve the fast string comment.
 - Improve the changelogs.

Andy Lutomirski (2):
  x86: Enable fast strings on Intel if BIOS hasn't already
  x86: Enable monitor/mwait on Intel if BIOS hasn't already

 arch/x86/kernel/cpu/intel.c |   52 ++++++++++++++++++++++++++++++++++++++----
 1 files changed, 47 insertions(+), 5 deletions(-)

-- 
1.7.6

[PATCH v3 1/2] x86: Enable fast strings on Intel if BIOS hasn't already

[Andy Lutomirski]

Intel SDM volume 3A, 8.4.2 says:

  Software can disable fast-string operation by clearing the
  fast-string-enable bit (bit 0) of IA32_MISC_ENABLE MSR.
  However, Intel recomments that system software always enable
  fast-string operation.

The Intel DQ67SW board (with latest BIOS) disables fast string
operations if TXT is enabled.  A Lenovo X220 disables it regardless
of TXT setting.  I doubt I'm the only person with a dumb BIOS like
this.

Signed-off-by: Andy Lutomirski <luto@mit.edu>
---
 arch/x86/kernel/cpu/intel.c |   28 +++++++++++++++++++++++-----
 1 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index ed6086e..7d02873 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -30,6 +30,7 @@
 static void __cpuinit early_init_intel(struct cpuinfo_x86 *c)
 {
 	u64 misc_enable;
+	bool allow_fast_string = true;
 
 	/* Unmask CPUID levels if masked: */
 	if (c->x86 > 6 || (c->x86 == 6 && c->x86_model >= 0xd)) {
@@ -118,10 +119,11 @@ static void __cpuinit early_init_intel(struct cpuinfo_x86 *c)
 	 * (model 2) with the same problem.
 	 */
 	if (c->x86 == 15) {
-		rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
+		allow_fast_string = false;
 
+		rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
 		if (misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING) {
-			printk(KERN_INFO "kmemcheck: Disabling fast string operations\n");
+			printk_once(KERN_INFO "kmemcheck: Disabling fast string operations\n");
 
 			misc_enable &= ~MSR_IA32_MISC_ENABLE_FAST_STRING;
 			wrmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
@@ -130,13 +132,29 @@ static void __cpuinit early_init_intel(struct cpuinfo_x86 *c)
 #endif
 
 	/*
-	 * If fast string is not enabled in IA32_MISC_ENABLE for any reason,
-	 * clear the fast string and enhanced fast string CPU capabilities.
+	 * If BIOS didn't enable fast string operation, try to enable
+	 * it ourselves.  If that fails, then clear the fast string
+	 * and enhanced fast string CPU capabilities.
 	 */
 	if (c->x86 > 6 || (c->x86 == 6 && c->x86_model >= 0xd)) {
 		rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
+
+		if (allow_fast_string &&
+		    !(misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING)) {
+			misc_enable |= MSR_IA32_MISC_ENABLE_FAST_STRING;
+			wrmsr_safe(MSR_IA32_MISC_ENABLE, (u32)misc_enable,
+				   (u32)(misc_enable >> 32));
+
+			/* Re-read to make sure it stuck. */
+			rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
+
+			if (misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING)
+				printk_once(KERN_INFO FW_WARN "CPU #%d: IA32_MISC_ENABLE.FAST_STRING_ENABLE was not set",
+				       c->cpu_index);
+		}
+
 		if (!(misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING)) {
-			printk(KERN_INFO "Disabled fast string operations\n");
+			printk_once(KERN_INFO "Failed to enable fast string operations\n");
 			setup_clear_cpu_cap(X86_FEATURE_REP_GOOD);
 			setup_clear_cpu_cap(X86_FEATURE_ERMS);
 		}
-- 
1.7.6

[PATCH v3 2/2] x86: Enable monitor/mwait on Intel if BIOS hasn't already

[Andy Lutomirski]

My Intel DQ67SW (latest BIOS) disables monitor/mwait on the boot CPU
if TXT is enabled.  We're lucky that the system works at all, since
the feature is still enabled on other CPUs.

The obvious fix is to just re-enable it ourselves.

Signed-off-by: Andy Lutomirski <luto@mit.edu>
---
 arch/x86/kernel/cpu/intel.c |   24 ++++++++++++++++++++++++
 1 files changed, 24 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 7d02873..c49487f 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -492,6 +492,30 @@ static void __cpuinit init_intel(struct cpuinfo_x86 *c)
 			wrmsrl(MSR_IA32_ENERGY_PERF_BIAS, epb);
 		}
 	}
+
+	/* Enable monitor/mwait if BIOS didn't do it for us. */
+	if (!cpu_has(c, X86_FEATURE_MWAIT) && cpu_has(c, X86_FEATURE_XMM3)
+	    && c->x86 >= 6 && !(c->x86 == 6 && c->x86_model < 0x1c)
+	    && !(c->x86 == 0xf && c->x86_model < 3)) {
+		u64 misc_enable;
+		rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
+		misc_enable |= MSR_IA32_MISC_ENABLE_MWAIT;
+
+		/*
+		 * Some non-SSE3 cpus will #GP.  We check for that,
+		 * but it can't hurt to be safe.
+		 */
+		wrmsr_safe(MSR_IA32_MISC_ENABLE, (u32)misc_enable,
+			   (u32)(misc_enable >> 32));
+
+		/* Re-read monitor capability. */
+		if (cpuid_ecx(1) & 0x8) {
+			set_cpu_cap(c, X86_FEATURE_MWAIT);
+
+			printk(KERN_WARNING FW_WARN "CPU #%d: IA32_MISC_ENABLE.ENABLE_MONITOR_FSM was not set\n",
+			       c->cpu_index);
+		}
+	}
 }
 
 #ifdef CONFIG_X86_32
-- 
1.7.6

Re: [PATCH v3 0/2] Forcibly enable some MISC_ENABLE features on Intel

[Alan Cox]

On Tue,  9 Aug 2011 08:41:04 -0400
Andy Lutomirski <luto@MIT.EDU> wrote:

> Intel allows BIOS or the OS to enable or disable some CPU fueatures via
> IA32_MISC_ENABLE.  I have machines that don't enable fast strings or
> monitor/mwait in BIOS, so do it on bootup instead.

The question is - why. 

> The Intel SDM volume 3, appendix B.1 says that the OS should not touch
> the monitor enable bit if SSE3 is not present, which presumably means
> that the OS may touch that bit if SSE3 is present.  In any case, these
> patches seem to work.

That's a big "presumes"

For example back in Pentium days the BIOS sometimes turned off a string
fast path because it was subtly not reliable on certain parts and could
corrupt.

It's possible your BIOS vendor has a good reason for doing this. It's
also possible its a bug, or a left over perhaps from some pre-release
processor or something.

I think a bit more research is probably appropriate before processor
configuration hacks go in that 'seem to work'.

Alan

Re: [PATCH v3 0/2] Forcibly enable some MISC_ENABLE features on Intel

[Andrew Lutomirski]

On Tue, Aug 9, 2011 at 8:50 AM, Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:
> On Tue,  9 Aug 2011 08:41:04 -0400
> Andy Lutomirski <luto@MIT.EDU> wrote:
>
>> Intel allows BIOS or the OS to enable or disable some CPU fueatures via
>> IA32_MISC_ENABLE.  I have machines that don't enable fast strings or
>> monitor/mwait in BIOS, so do it on bootup instead.
>
> The question is - why.
>
>> The Intel SDM volume 3, appendix B.1 says that the OS should not touch
>> the monitor enable bit if SSE3 is not present, which presumably means
>> that the OS may touch that bit if SSE3 is present.  In any case, these
>> patches seem to work.
>
> That's a big "presumes"
>
> For example back in Pentium days the BIOS sometimes turned off a string
> fast path because it was subtly not reliable on certain parts and could
> corrupt.
>
> It's possible your BIOS vendor has a good reason for doing this. It's
> also possible its a bug, or a left over perhaps from some pre-release
> processor or something.

Intel also says:

  However, Intel recomments that system software always enable
  fast-string operation.

On my machine it's definitely a bug.  It's a Sandy Bridge box (from
Intel) and with TXT disabled the BIOS enables fast strings on its own.

Fenghua, do you know if there are any machines that will pass the
version checks and will actually allow fast strings to be enabled but
that will have problems as a result?

If we want to be conservative, we could limit it to the most recent
family 6 devices and exclude family 0xf entirely.

--Andy

RE: [PATCH v3 1/2] x86: Enable fast strings on Intel if BIOS hasn't already

[Yu, Fenghua]

> -----Original Message-----
> From: Andy Lutomirski [mailto:luto@MIT.EDU]
> Sent: Tuesday, August 09, 2011 5:41 AM
> To: x86@kernel.org; linux-kernel@vger.kernel.org
> Cc: Yu, Fenghua; Matthew Garrett; Len Brown; linux-
> acpi@vger.kernel.org; Ingo Molnar; Andy Lutomirski
> Subject: [PATCH v3 1/2] x86: Enable fast strings on Intel if BIOS
> hasn't already
> 
> Intel SDM volume 3A, 8.4.2 says:
> 
>   Software can disable fast-string operation by clearing the
>   fast-string-enable bit (bit 0) of IA32_MISC_ENABLE MSR.
>   However, Intel recomments that system software always enable
>   fast-string operation.
> 
> The Intel DQ67SW board (with latest BIOS) disables fast string
> operations if TXT is enabled.  A Lenovo X220 disables it regardless
> of TXT setting.  I doubt I'm the only person with a dumb BIOS like
> this.
> 
> Signed-off-by: Andy Lutomirski <luto@mit.edu>
> ---
>  arch/x86/kernel/cpu/intel.c |   28 +++++++++++++++++++++++-----
>  1 files changed, 23 insertions(+), 5 deletions(-)

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>

Re: [PATCH v3 1/2] x86: Enable fast strings on Intel if BIOS hasn't already

[Andrew Lutomirski]

On Tue, Aug 9, 2011 at 11:40 AM, Yu, Fenghua <fenghua.yu@intel.com> wrote:
>> -----Original Message-----
>> From: Andy Lutomirski [mailto:luto@MIT.EDU]
>> Sent: Tuesday, August 09, 2011 5:41 AM
>> To: x86@kernel.org; linux-kernel@vger.kernel.org
>> Cc: Yu, Fenghua; Matthew Garrett; Len Brown; linux-
>> acpi@vger.kernel.org; Ingo Molnar; Andy Lutomirski
>> Subject: [PATCH v3 1/2] x86: Enable fast strings on Intel if BIOS
>> hasn't already
>>
>> Intel SDM volume 3A, 8.4.2 says:
>>
>>   Software can disable fast-string operation by clearing the
>>   fast-string-enable bit (bit 0) of IA32_MISC_ENABLE MSR.
>>   However, Intel recomments that system software always enable
>>   fast-string operation.
>>
>> The Intel DQ67SW board (with latest BIOS) disables fast string
>> operations if TXT is enabled.  A Lenovo X220 disables it regardless
>> of TXT setting.  I doubt I'm the only person with a dumb BIOS like
>> this.
>>
>> Signed-off-by: Andy Lutomirski <luto@mit.edu>
>> ---
>>  arch/x86/kernel/cpu/intel.c |   28 +++++++++++++++++++++++-----
>>  1 files changed, 23 insertions(+), 5 deletions(-)
>
> Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
>
>

Please don't apply.  This patch breaks !CONFIG_SMP.  I'll send a fixed
patch later on.

--Andy

RE: [PATCH v3 1/2] x86: Enable fast strings on Intel if BIOS hasn't already

[Yu, Fenghua]

> -----Original Message-----
> From: amluto@gmail.com [mailto:amluto@gmail.com] On Behalf Of Andrew
> Lutomirski
> Sent: Wednesday, August 10, 2011 7:50 AM
> To: Yu, Fenghua
> Cc: x86@kernel.org; linux-kernel@vger.kernel.org; Matthew Garrett; Len
> Brown; linux-acpi@vger.kernel.org; Ingo Molnar; Anvin, H Peter
> Subject: Re: [PATCH v3 1/2] x86: Enable fast strings on Intel if BIOS
> hasn't already
> 
> On Tue, Aug 9, 2011 at 11:40 AM, Yu, Fenghua <fenghua.yu@intel.com>
> wrote:
> >> -----Original Message-----
> >> From: Andy Lutomirski [mailto:luto@MIT.EDU]
> >> Sent: Tuesday, August 09, 2011 5:41 AM
> >> To: x86@kernel.org; linux-kernel@vger.kernel.org
> >> Cc: Yu, Fenghua; Matthew Garrett; Len Brown; linux-
> >> acpi@vger.kernel.org; Ingo Molnar; Andy Lutomirski
> >> Subject: [PATCH v3 1/2] x86: Enable fast strings on Intel if BIOS
> >> hasn't already
> >>
> >> Intel SDM volume 3A, 8.4.2 says:
> >>
> >>   Software can disable fast-string operation by clearing the
> >>   fast-string-enable bit (bit 0) of IA32_MISC_ENABLE MSR.
> >>   However, Intel recomments that system software always enable
> >>   fast-string operation.
> >>
> >> The Intel DQ67SW board (with latest BIOS) disables fast string
> >> operations if TXT is enabled.  A Lenovo X220 disables it regardless
> >> of TXT setting.  I doubt I'm the only person with a dumb BIOS like
> >> this.
> >>
> >> Signed-off-by: Andy Lutomirski <luto@mit.edu>
> >> ---
> >>  arch/x86/kernel/cpu/intel.c |   28 +++++++++++++++++++++++-----
> >>  1 files changed, 23 insertions(+), 5 deletions(-)
> >
> > Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
> >
> >
> 
> Please don't apply.  This patch breaks !CONFIG_SMP.  I'll send a fixed
> patch later on.

+				printk_once(KERN_INFO FW_WARN "CPU #%d: IA32_MISC_ENABLE.FAST_STRING_ENABLE was not set",
There is no need to print CPU id. Then there is no SMP issue.

Thanks.

-Fenghua

Re: [PATCH v3 1/2] x86: Enable fast strings on Intel if BIOS hasn't already

[Andrew Lutomirski]

On Wed, Aug 10, 2011 at 11:05 AM, Yu, Fenghua <fenghua.yu@intel.com> wrote:
>> -----Original Message-----
>> From: amluto@gmail.com [mailto:amluto@gmail.com] On Behalf Of Andrew
>> Lutomirski
>> Sent: Wednesday, August 10, 2011 7:50 AM
>> To: Yu, Fenghua
>> Cc: x86@kernel.org; linux-kernel@vger.kernel.org; Matthew Garrett; Len
>> Brown; linux-acpi@vger.kernel.org; Ingo Molnar; Anvin, H Peter
>> Subject: Re: [PATCH v3 1/2] x86: Enable fast strings on Intel if BIOS
>> hasn't already
>>
>> On Tue, Aug 9, 2011 at 11:40 AM, Yu, Fenghua <fenghua.yu@intel.com>
>> wrote:
>> >> -----Original Message-----
>> >> From: Andy Lutomirski [mailto:luto@MIT.EDU]
>> >> Sent: Tuesday, August 09, 2011 5:41 AM
>> >> To: x86@kernel.org; linux-kernel@vger.kernel.org
>> >> Cc: Yu, Fenghua; Matthew Garrett; Len Brown; linux-
>> >> acpi@vger.kernel.org; Ingo Molnar; Andy Lutomirski
>> >> Subject: [PATCH v3 1/2] x86: Enable fast strings on Intel if BIOS
>> >> hasn't already
>> >>
>> >> Intel SDM volume 3A, 8.4.2 says:
>> >>
>> >>   Software can disable fast-string operation by clearing the
>> >>   fast-string-enable bit (bit 0) of IA32_MISC_ENABLE MSR.
>> >>   However, Intel recomments that system software always enable
>> >>   fast-string operation.
>> >>
>> >> The Intel DQ67SW board (with latest BIOS) disables fast string
>> >> operations if TXT is enabled.  A Lenovo X220 disables it regardless
>> >> of TXT setting.  I doubt I'm the only person with a dumb BIOS like
>> >> this.
>> >>
>> >> Signed-off-by: Andy Lutomirski <luto@mit.edu>
>> >> ---
>> >>  arch/x86/kernel/cpu/intel.c |   28 +++++++++++++++++++++++-----
>> >>  1 files changed, 23 insertions(+), 5 deletions(-)
>> >
>> > Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
>> >
>> >
>>
>> Please don't apply.  This patch breaks !CONFIG_SMP.  I'll send a fixed
>> patch later on.
>
> +                               printk_once(KERN_INFO FW_WARN "CPU #%d: IA32_MISC_ENABLE.FAST_STRING_ENABLE was not set",
> There is no need to print CPU id. Then there is no SMP issue.

True, and with the printk_once change it's pointless.  I was printing
it because of the other patch: my BIOS enables monitor/mwait on some,
but not all, CPUs.  (Working around that is a little less optional.
My systems gets lucky because it's off on the boot CPU so the idle
loop doesn't call mwait.  If it were the other way around, the kernel
would presumably oops quickly.)

--Andy

Re: [PATCH v3 0/2] Forcibly enable some MISC_ENABLE features on Intel

[Len Brown]

Andrew,

FWIW,
Intel's internal bug database claims this issue on your board
is fixed in the next BIOS update.

thanks,
Len Brown, Intel Open Source Technology Center

Re: [PATCH v3 0/2] Forcibly enable some MISC_ENABLE features on Intel

[Andrew Lutomirski]

On Wed, Aug 10, 2011 at 2:21 PM, Len Brown <lenb@kernel.org> wrote:
> Andrew,
>
> FWIW,
> Intel's internal bug database claims this issue on your board
> is fixed in the next BIOS update.

Yay for fixes.  But the FW_WARN might get these things noticed and fixed sooner.

Also, the fast string issue is present in Lenovo machines, too, so
Intel can't fix them all.

--Andy