From: Andi Kleen <a...@linux.intel.com>
For testing purposes it can be useful to downgrade microcode.
Normally the driver only allows upgrading.
Add a module_param (default off) that allows downgrading.
Note the module_param can currently not be set for early
ucode update, only for late.
Signed-off-by: Andi Kleen <a...@linux.intel.com>
---
arch/x86/kernel/microcode_intel_lib.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/arch/x86/kernel/microcode_intel_lib.c
b/arch/x86/kernel/microcode_intel_lib.c
index ce69320..18d5325 100644
--- a/arch/x86/kernel/microcode_intel_lib.c
+++ b/arch/x86/kernel/microcode_intel_lib.c
@@ -26,11 +26,16 @@
#include <linux/uaccess.h>
#include <linux/kernel.h>
#include <linux/module.h>
+#include <linux/moduleparam.h>
#include <asm/microcode_intel.h>
#include <asm/processor.h>
#include <asm/msr.h>
+static bool allow_downgrade;
+module_param(allow_downgrade, bool, 0644);
+MODULE_PARM_DESC(allow_downgrade, "Allow downgrading microcode");
+
static inline int
update_match_cpu(unsigned int csig, unsigned int cpf,
unsigned int sig, unsigned int pf)
@@ -41,6 +46,8 @@ update_match_cpu(unsigned int csig, unsigned int cpf,
int
update_match_revision(struct microcode_header_intel *mc_header, int rev)
{
+ if (allow_downgrade)
+ return 1;
return (mc_header->rev <= rev) ? 0 : 1;
}
--
1.8.3.1
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