[PATCH 08/14] i8k: Force SMM to run on CPU 0

Guenter Roeck
2013-12-14T17:31:23Z

On Studio 1555 with dual-core CPU, reading sensor attributes
exported by this driver resulted in random failures combined
with system hangups and forced logouts. Information in
drivers/firmware/dcdbas.c suggests that SMM accesses must
run on CPU 0. With this patch, the problems are gone,
suggesting that this is in fact the case.

Code derived from drivers/firmware/dcdbas.c.

Cc: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
drivers/char/i8k.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/char/i8k.c b/drivers/char/i8k.c
index ad0acef..264be2b 100644
--- a/drivers/char/i8k.c
+++ b/drivers/char/i8k.c
@@ -31,6 +31,7 @@
#include <linux/hwmon-sysfs.h>
#include <linux/uaccess.h>
#include <linux/io.h>
+#include <linux/sched.h>

#include <linux/i8k.h>

@@ -130,6 +131,17 @@ static int i8k_smm(struct smm_regs *regs)
{
int rc;
int eax = regs->eax;
+ cpumask_var_t old_mask;
+
+ /* SMM requires CPU 0 */
+ if (!alloc_cpumask_var(&old_mask, GFP_KERNEL))
+ return -ENOMEM;
+ cpumask_copy(old_mask, &current->cpus_allowed);
+ set_cpus_allowed_ptr(current, cpumask_of(0));
+ if (smp_processor_id() != 0) {
+ rc = -EBUSY;
+ goto out;
+ }

#if defined(CONFIG_X86_64)
asm volatile("pushq %%rax\n\t"
@@ -185,9 +197,12 @@ static int i8k_smm(struct smm_regs *regs)
: "%ebx", "%ecx", "%edx", "%esi", "%edi", "memory");
#endif
if (rc != 0 || (regs->eax & 0xffff) == 0xffff || regs->eax == eax)
- return -EINVAL;
+ rc = -EINVAL;

- return 0;
+out:
+ set_cpus_allowed_ptr(current, old_mask);
+ free_cpumask_var(old_mask);
+ return rc;
}

/*
--
1.7.9.7