Re: [patch V4 15/30] x86/microcode: Remove pointless apply() invocation

[Borislav Petkov]

On Mon, Oct 02, 2023 at 01:59:52PM +0200, Thomas Gleixner wrote:
> Microcode is applied on the APs during early bringup. There is no point in
> trying to apply the microcode again during the hotplug operations and
> neither at the point where the microcode device is initialized.
> 
> Collect CPU info and microcode revision in setup_online_cpu() for now. This
> will move to the CPU hotplug callback in the next step.
> 
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> ---
> V2: New patch
> ---
>  arch/x86/kernel/cpu/microcode/core.c |   34 ++++++----------------------------
>  include/linux/cpuhotplug.h           |    1 -
>  2 files changed, 6 insertions(+), 29 deletions(-)

Partial revert, as discussed. I've left enough breadcrumbs in case we
wanna tackle this again in the future:

---
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date: Mon, 2 Oct 2023 13:59:52 +0200
Subject: [PATCH] x86/microcode: Remove pointless apply() invocation

Microcode is applied on the APs during early bringup. There is no point
in trying to apply the microcode again during the hotplug operations and
neither at the point where the microcode device is initialized.

Collect CPU info and microcode revision in setup_online_cpu() for now.
This will move to the CPU hotplug callback later.

  [ bp: Leave the starting notifier for the following scenario:

    - boot, late load, suspend to disk, resume

    without the starting notifier, only the last core manages to update the
    microcode upon resume:

    # rdmsr -a 0x8b
    10000bf
    10000bf
    10000bf
    10000bf
    10000bf
    10000dc <----

    This is on an AMD F10h machine.

    For the future, one should check whether potential unification of
    the CPU init path could cover the resume path too so that this can
    be simplified even more. ]

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Link: https://lore.kernel.org/r/20231002115902.914469212@xxxxxxxxxxxxx
---
 arch/x86/kernel/cpu/microcode/core.c | 23 ++++++-----------------
 1 file changed, 6 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 0d99d5eab3fc..6f7632fa2e61 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -490,17 +490,6 @@ static void microcode_fini_cpu(int cpu)
 		microcode_ops->microcode_fini_cpu(cpu);
 }
 
-static enum ucode_state microcode_init_cpu(int cpu)
-{
-	struct ucode_cpu_info *uci = ucode_cpu_info + cpu;
-
-	memset(uci, 0, sizeof(*uci));
-
-	microcode_ops->collect_cpu_info(cpu, &uci->cpu_sig);
-
-	return microcode_ops->apply_microcode(cpu);
-}
-
 /**
  * microcode_bsp_resume - Update boot CPU microcode during resume.
  */
@@ -555,14 +544,14 @@ static int mc_cpu_down_prep(unsigned int cpu)
 static void setup_online_cpu(struct work_struct *work)
 {
 	int cpu = smp_processor_id();
-	enum ucode_state err;
+	struct ucode_cpu_info *uci = ucode_cpu_info + cpu;
 
-	err = microcode_init_cpu(cpu);
-	if (err == UCODE_ERROR) {
-		pr_err("Error applying microcode on CPU%d\n", cpu);
-		return;
-	}
+	memset(uci, 0, sizeof(*uci));
 
+	microcode_ops->collect_cpu_info(cpu, &uci->cpu_sig);
+	cpu_data(cpu).microcode = uci->cpu_sig.rev;
+	if (!cpu)
+		boot_cpu_data.microcode = uci->cpu_sig.rev;
 	mc_cpu_online(cpu);
 }
 
-- 
2.42.0.rc0.25.ga82fb66fed25

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette