Re: [PATCH 1/1] arch/x86/microcode/intel: Remove unnecessary cache writeback and invalidation

[Chang S. Bae]

On 7/3/2024 2:33 PM, Ashok Raj wrote:
> When wbinvd() was introduced I do believe we added to both early and late.
> Although I don't recall entirely.

Yes, it was added for both:

$ git show --source 91df9fdf5149
...
diff --git a/arch/x86/kernel/cpu/microcode/intel.c 
b/arch/x86/kernel/cpu/microcode/intel.c
index 87bd6dc94081..e2864bc2d575 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -600,6 +600,12 @@ static int apply_microcode_early(struct 
ucode_cpu_info *uci, bool early)
                return UCODE_OK;
        }

+       /*
+        * Writeback and invalidate caches before updating microcode to 
avoid
+        * internal issues depending on what the microcode is updating.
+        */
+       native_wbinvd();
+
        /* write microcode via MSR 0x79 */
        native_wrmsrl(MSR_IA32_UCODE_WRITE, (unsigned long)mc->bits);

@@ -816,6 +822,12 @@ static enum ucode_state apply_microcode_intel(int cpu)
                return UCODE_OK;
        }

+       /*
+        * Writeback and invalidate caches before updating microcode to 
avoid
+        * internal issues depending on what the microcode is updating.
+        */
+       native_wbinvd();
+
        /* write microcode via MSR 0x79 */
        wrmsrl(MSR_IA32_UCODE_WRITE, (unsigned long)mc->bits);

Thanks,
Chang