Re: [PATCH] x86, therm: Only read the initial value of thermal LVT entry on BSP

[Suresh Siddha <suresh.b.siddha@intel.com>]

On Fri, 2009-11-06 at 16:17 -0800, Yong Wang wrote:
> Only read the initial value of thermal LVT entry on BSP. The initial
> value of thermal LVT entries on all APs always reads 0x10000 because
> APs are woken up by BSP issuing INIT-SIPI-SIPI sequence to them and
> LVT registers are reset to 0s except for mask bits which are set to
> 1s when APs receive INIT IPI.
> 
> Also restore the value that BIOS has programmed on AP based on BSP's
> info we saved since BIOS is always setting the same value for all
> threads/cores.

Yong, I have appended a new patch with an enhanced change log and
subject. In future, when you modify and post another version of the
patch, can you please update the patch version and elaborate what has
changed, why etc, so that it will be easier for the reviewers.

Ingo/Peter, please review and queue this patch from Yong. Thanks.
---

From: Yong Wang <yong.y.wang@intel.com>
Subject: x86: under bios control, restore AP's APIC_LVTTHMR to the BSP value

On platforms where bios handles the thermal monitor interrupt,
APIC_LVTTHMR on each logical CPU is programmed to generate a SMI and OS
can't touch it.

Unfortunately AP bringup sequence using INIT-SIPI-SIPI clear all
the LVT entries except the mask bit. Essentially this results in
all LVT entries including the thermal monitoring interrupt set to masked
(clearing the bios programmed value for APIC_LVTTHMR).

And this leads to kernel take over the thermal monitoring interrupt
on AP's but not on BSP (leaving the bios programmed value only on BSP).

As a result of this, we have seen system hangs when the thermal
monitoring interrupt is generated.

Fix this by reading the initial value of thermal LVT entry on BSP
and if bios has taken over the control, then program the same value
on all AP's and leave the thermal monitoring interrupt control
on all the logical cpu's to the bios.

Signed-off-by: Yong Wang <yong.y.wang@intel.com>
Reviewed-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: stable@kernel.org
---
 arch/x86/kernel/cpu/mcheck/therm_throt.c |   20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/mcheck/therm_throt.c b/arch/x86/kernel/cpu/mcheck/therm_throt.c
index b3a1dba..1fd42db 100644
--- a/arch/x86/kernel/cpu/mcheck/therm_throt.c
+++ b/arch/x86/kernel/cpu/mcheck/therm_throt.c
@@ -259,6 +259,7 @@ void intel_init_thermal(struct cpuinfo_x86 *c)
 	unsigned int cpu = smp_processor_id();
 	int tm2 = 0;
 	u32 l, h;
+	static u32 lvtthmr;
 
 	/* Thermal monitoring depends on ACPI and clock modulation*/
 	if (!cpu_has(c, X86_FEATURE_ACPI) || !cpu_has(c, X86_FEATURE_ACC))
@@ -270,7 +271,24 @@ void intel_init_thermal(struct cpuinfo_x86 *c)
 	 * since it might be delivered via SMI already:
 	 */
 	rdmsr(MSR_IA32_MISC_ENABLE, l, h);
-	h = apic_read(APIC_LVTTHMR);
+
+	/*
+	 * Only read the initial value of thermal LVT entry on BSP. The
+	 * initial value of thermal LVT entries on all APs always reads
+	 * 0x10000 because APs are woken up by BSP issuing INIT-SIPI-SIPI
+	 * sequence to them and LVT registers are reset to 0s except for
+	 * the mask bits which are set to 1s when APs receive INIT IPI.
+	 * Also restore the value that BIOS has programmed on AP based on
+	 * BSP's info we saved since BIOS is always setting the same value
+	 * for all threads/cores
+	 */
+	if (cpu == 0)
+		lvtthmr = apic_read(APIC_LVTTHMR);
+	else
+		apic_write(APIC_LVTTHMR, lvtthmr);
+
+	h = lvtthmr;
+
 	if ((l & MSR_IA32_MISC_ENABLE_TM1) && (h & APIC_DM_SMI)) {
 		printk(KERN_DEBUG
 		       "CPU%d: Thermal monitoring handled by SMI\n", cpu);