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Subject[Patch V1 4/7] x86/microcode/core: Take a snapshot before and after applying microcode
Date
The kernel caches features about each CPU's features at boot in an
x86_capability[] structure. The microcode update takes one snapshot and
compares it with the saved copy at boot.

However, the capabilities in the boot copy can be turned off as a result of
certain command line parameters or configuration restrictions. This can
cause a mismatch when comparing the values before and after the microcode
update.

microcode_check() is called after an update to report any previously
cached CPUID bits might have changed due to the update.

Ignore the capabilities recorded at boot. Take a new snapshot before the
update and compare with a snapshot after the update to eliminate the false
warning.

Fixes: 1008c52c09dc ("x86/CPU: Add a microcode loader callback")
Signed-off-by: Ashok Raj <ashok.raj@intel.com>
---
arch/x86/kernel/cpu/microcode/core.c | 36 ++++++++++++++++++++--------
1 file changed, 26 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index ef24e1d228d0..fab2010ff368 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -431,12 +431,28 @@ static int __reload_late(void *info)
return ret;
}

+static void copy_cpu_caps(struct cpuinfo_x86 *info)
+{
+ /* Reload CPUID max function as it might've changed. */
+ info->cpuid_level = cpuid_eax(0);
+
+ /*
+ * Copy all capability leafs to pick up the synthetic ones so that
+ * memcmp() below doesn't fail on that. The ones coming from CPUID will
+ * get overwritten in get_cpu_cap().
+ */
+ memcpy(info->x86_capability, &boot_cpu_data.x86_capability,
+ sizeof(info->x86_capability));
+
+ get_cpu_cap(info);
+}
+
/*
* The microcode loader calls this upon late microcode load to recheck features,
* only when microcode has been updated. Caller holds microcode_mutex and CPU
* hotplug lock.
*/
-static void microcode_check(void)
+static void microcode_check(struct cpuinfo_x86 *orig)
{
struct cpuinfo_x86 info;

@@ -446,15 +462,13 @@ static void microcode_check(void)
info.cpuid_level = cpuid_eax(0);

/*
- * Copy all capability leafs to pick up the synthetic ones so that
- * memcmp() below doesn't fail on that. The ones coming from CPUID will
- * get overwritten in get_cpu_cap().
- */
- memcpy(&info.x86_capability, &boot_cpu_data.x86_capability, sizeof(info.x86_capability));
+ * Copy all capability leafs to pick up the synthetic ones so that
+ * memcmp() below doesn't fail on that. The ones coming from CPUID will
+ * get overwritten in get_cpu_cap().
+ */
+ copy_cpu_caps(&info);

- get_cpu_cap(&info);
-
- if (!memcmp(&info.x86_capability, &boot_cpu_data.x86_capability,
+ if (!memcmp(&info.x86_capability, &orig->x86_capability,
sizeof(info.x86_capability)))
return;

@@ -469,6 +483,7 @@ static void microcode_check(void)
static int microcode_reload_late(void)
{
int old = boot_cpu_data.microcode, ret;
+ struct cpuinfo_x86 info;

pr_err("Attempting late microcode loading - it is dangerous and taints the kernel.\n");
pr_err("You should switch to early loading, if possible.\n");
@@ -476,9 +491,10 @@ static int microcode_reload_late(void)
atomic_set(&late_cpus_in, 0);
atomic_set(&late_cpus_out, 0);

+ copy_cpu_caps(&info);
ret = stop_machine_cpuslocked(__reload_late, NULL, cpu_online_mask);
if (ret == 0)
- microcode_check();
+ microcode_check(&info);

pr_info("Reload completed, microcode revision: 0x%x -> 0x%x\n",
old, boot_cpu_data.microcode);
--
2.34.1
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