On Intel it is required to do CPUID(1) before reading the microcode revision MSR. Current code in 4.4 an 4.9 relies on sync_core() to call CPUID, unfortunately on 32 bit machines code inside sync_core() always jumps past CPUID instruction as it depends on data structure boot_cpu_data witch are not populated correctly so early in boot sequence.

It depends on: commit 5dedade6dfa2 ("x86/CPU: Add native CPUID variants returning a single datum")

This patch is for 4.4 but also should apply to 4.9

Signed-off-by: Evalds Iodzevics evalds.iodzevics@gmail.com Cc: stable@vger.kernel.org --- arch/x86/include/asm/microcode_intel.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/microcode_intel.h b/arch/x86/include/asm/microcode_intel.h index 90343ba50485..92ce9c8a508b 100644 --- a/arch/x86/include/asm/microcode_intel.h +++ b/arch/x86/include/asm/microcode_intel.h @@ -60,7 +60,7 @@ static inline u32 intel_get_microcode_revision(void) native_wrmsrl(MSR_IA32_UCODE_REV, 0);

/* As documented in the SDM: Do a CPUID 1 here */ - sync_core(); + native_cpuid_eax(1);

/* get the current revision from MSR 0x8B */ native_rdmsr(MSR_IA32_UCODE_REV, dummy, rev);