[patch 19/30] x86/microcode: Clarify the late load logic

From: Thomas Gleixner
Date: Thu Aug 10 2023 - 14:39:02 EST


From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

reload_store() is way too complicated. Split the inner workings out and
make the following enhancements:

- Taint the kernel only when the microcode was actually updated. If. e.g.
the rendevouz fails, then nothing happened and there is no reason for
tainting.

- Return useful error codes

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

---
arch/x86/kernel/cpu/microcode/core.c | 39 +++++++++++++++--------------------
1 file changed, 17 insertions(+), 22 deletions(-)
---
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -434,11 +434,11 @@ static int microcode_reload_late(void)
pr_info("Reload succeeded, microcode revision: 0x%x -> 0x%x\n",
old, boot_cpu_data.microcode);
microcode_check(&prev_info);
+ add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
} else {
pr_info("Reload failed, current microcode revision: 0x%x\n",
boot_cpu_data.microcode);
}
-
return ret;
}

@@ -471,40 +471,35 @@ static bool ensure_cpus_are_online(void)
return true;
}

+static int ucode_load_late_locked(void)
+{
+ int ret;
+
+ if (!ensure_cpus_are_online())
+ return -EBUSY;
+
+ ret = microcode_ops->request_microcode_fw(0, &microcode_pdev->dev);
+ if (ret != UCODE_NEW)
+ return ret == UCODE_NFOUND ? -ENOENT : -EBADFD;
+ return microcode_reload_late();
+}
+
static ssize_t reload_store(struct device *dev,
struct device_attribute *attr,
const char *buf, size_t size)
{
- enum ucode_state tmp_ret = UCODE_OK;
- int bsp = boot_cpu_data.cpu_index;
unsigned long val;
- ssize_t ret = 0;
+ ssize_t ret;

ret = kstrtoul(buf, 0, &val);
if (ret || val != 1)
return -EINVAL;

cpus_read_lock();
-
- if (!ensure_cpus_are_online()) {
- ret = -EBUSY;
- goto put;
- }
-
- tmp_ret = microcode_ops->request_microcode_fw(bsp, &microcode_pdev->dev);
- if (tmp_ret != UCODE_NEW)
- goto put;
-
- ret = microcode_reload_late();
-put:
+ ret = ucode_load_late_locked();
cpus_read_unlock();

- if (ret == 0)
- ret = size;
-
- add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
-
- return ret;
+ return ret ? : size;
}

static DEVICE_ATTR_WO(reload);