Re: [Patch V1 4/7] x86/microcode/core: Take a snapshot before and after applying microcode
From: Thomas Gleixner
Date: Fri Dec 02 2022 - 14:09:37 EST
On Tue, Nov 29 2022 at 13:08, Ashok Raj wrote:
> 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.
Makes sense.
> +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);
You clearly ran out of newlines and comments here.
> if (ret == 0)
> - microcode_check();
> + microcode_check(&info);
>
> pr_info("Reload completed, microcode revision: 0x%x -> 0x%x\n",
> old, boot_cpu_data.microcode);
Unrelated to that patch, but it just caught my attention. Why are we
printing this is case of failure?
Thanks,
tglx