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Subject[PATCH 9/10] work_on_cpu: use on drivers/firmware/dcdbas.c

Impact: don't play with current's cpumask

It's generally a very bad idea to mug some process's cpumask: it could
legitimately and reasonably be changed by root, which could break us
(if done before our code) or them (if we restore the wrong value).

So we use work_on_cpu instead of cpumask games.

Note one subtle change. If we can't get to CPU 0 for some reason, the
return will be -EINVAL not -EBUSY. We could fix this in the
caller? ie:

return work_on_cpu(0, generate_smi, smi_cmd) == 0 ? 0 : -EBUSY;

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Cc: Matt Domsch <Matt_Domsch@dell.com>
Cc: Douglas_Warzecha@dell.com
---
drivers/firmware/dcdbas.c | 46 +++++++++++++++++++---------------------------
1 file changed, 19 insertions(+), 27 deletions(-)

diff --git a/drivers/firmware/dcdbas.c b/drivers/firmware/dcdbas.c
--- a/drivers/firmware/dcdbas.c
+++ b/drivers/firmware/dcdbas.c
@@ -237,31 +237,9 @@ static ssize_t host_control_on_shutdown_
return count;
}

-/**
- * dcdbas_smi_request: generate SMI request
- *
- * Called with smi_data_lock.
- */
-int dcdbas_smi_request(struct smi_cmd *smi_cmd)
+static long generate_smi(void *_smi_cmd)
{
- cpumask_t old_mask;
- int ret = 0;
-
- if (smi_cmd->magic != SMI_CMD_MAGIC) {
- dev_info(&dcdbas_pdev->dev, "%s: invalid magic value\n",
- __func__);
- return -EBADR;
- }
-
- /* SMI requires CPU 0 */
- old_mask = current->cpus_allowed;
- set_cpus_allowed_ptr(current, &cpumask_of_cpu(0));
- if (smp_processor_id() != 0) {
- dev_dbg(&dcdbas_pdev->dev, "%s: failed to get CPU 0\n",
- __func__);
- ret = -EBUSY;
- goto out;
- }
+ struct smi_cmd *smi_cmd = _smi_cmd;

/* generate SMI */
asm volatile (
@@ -273,10 +251,24 @@ int dcdbas_smi_request(struct smi_cmd *s
"c" (smi_cmd->ecx)
: "memory"
);
+ return 0;
+}

-out:
- set_cpus_allowed_ptr(current, &old_mask);
- return ret;
+/**
+ * dcdbas_smi_request: generate SMI request
+ *
+ * Called with smi_data_lock.
+ */
+int dcdbas_smi_request(struct smi_cmd *smi_cmd)
+{
+ if (smi_cmd->magic != SMI_CMD_MAGIC) {
+ dev_info(&dcdbas_pdev->dev, "%s: invalid magic value\n",
+ __func__);
+ return -EBADR;
+ }
+
+ /* SMI requires CPU 0 */
+ return work_on_cpu(0, generate_smi, smi_cmd);
}

/**


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