Messages in this thread Patch in this message | | | From | Ashok Raj <> | Subject | [PATCH v4 2/6] x86/microcode/core: Take a snapshot before and after applying microcode | Date | Mon, 9 Jan 2023 07:35:51 -0800 |
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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.
store_cpu_caps() basically stores the original CPU reported values and not the OS modified values. This will avoid giving a false warning even when no capabilities have changed.
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.
Signed-off-by: Ashok Raj <ashok.raj@intel.com> Fixes: 1008c52c09dc ("x86/CPU: Add a microcode loader callback") Cc: LKML <linux-kernel@vger.kernel.org> Cc: x86 <x86@kernel.org> Cc: Tony Luck <tony.luck@intel.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Alison Schofield <alison.schofield@intel.com> Cc: Reinette Chatre <reinette.chatre@intel.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tom Lendacky <thomas.lendacky@amd.com> Cc: Ingo Molnar <mingo@kernel.org> --- Changes since V3: - Boris - Change function from microcode_store_cpu_caps -> store_cpu_caps - Split comments in store_cpu_caps().
- Dave Hansen - Change parameters names to something meaninful. - Cleaned up some commit log.
Changes since V2:
- Boris - Keep microcode_check() inside cpu/common.c and not bleed get_cpu_caps() outside of core code.
- Thomas - Commit log changes. --- arch/x86/include/asm/processor.h | 1 + arch/x86/kernel/cpu/common.c | 39 ++++++++++++++++++++-------- arch/x86/kernel/cpu/microcode/core.c | 7 +++++ 3 files changed, 36 insertions(+), 11 deletions(-)
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index f256a4ddd25d..a77dee6a2bf2 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -698,6 +698,7 @@ bool xen_set_default_idle(void); void __noreturn stop_this_cpu(void *dummy); void microcode_check(struct cpuinfo_x86 *prev_info); +void store_cpu_caps(struct cpuinfo_x86 *info); enum l1tf_mitigations { L1TF_MITIGATION_OFF, diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 0f5a173d0871..f5c6feed6c26 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -2297,6 +2297,29 @@ void cpu_init_secondary(void) #endif #ifdef CONFIG_MICROCODE_LATE_LOADING +/** + * store_cpu_caps() - Store a snapshot of CPU capabilities + * + * Returns: None + */ +void store_cpu_caps(struct cpuinfo_x86 *curr_info) +{ + /* Reload CPUID max function as it might've changed. */ + curr_info->cpuid_level = cpuid_eax(0); + + /* + * Copy all capability leafs to pick up the synthetic ones + */ + memcpy(&curr_info->x86_capability, &boot_cpu_data.x86_capability, + sizeof(curr_info->x86_capability)); + + /* + * Capabilities copied from BSP will get overwritten + * with the snapshot below + */ + get_cpu_cap(curr_info); +} + /** * microcode_check() - Check if any CPU capabilities changed after an update. * @prev_info: CPU capabilities stored before an update. @@ -2309,22 +2332,16 @@ void cpu_init_secondary(void) */ void microcode_check(struct cpuinfo_x86 *prev_info) { - perf_check_microcode(); + struct cpuinfo_x86 curr_info; - /* Reload CPUID max function as it might've changed. */ - prev_info->cpuid_level = cpuid_eax(0); + perf_check_microcode(); /* - * 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(). + * Get a snapshot of CPU capabilities */ - memcpy(&prev_info->x86_capability, &boot_cpu_data.x86_capability, - sizeof(prev_info->x86_capability)); - - get_cpu_cap(prev_info); + store_cpu_caps(&curr_info); - if (!memcmp(&prev_info->x86_capability, &boot_cpu_data.x86_capability, + if (!memcmp(&prev_info->x86_capability, &curr_info.x86_capability, sizeof(prev_info->x86_capability))) return; diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c index e39d83be794b..bb943a91a364 100644 --- a/arch/x86/kernel/cpu/microcode/core.c +++ b/arch/x86/kernel/cpu/microcode/core.c @@ -447,6 +447,13 @@ static int microcode_reload_late(void) atomic_set(&late_cpus_in, 0); atomic_set(&late_cpus_out, 0); + /* + * Take a snapshot before the microcode update, so we can compare + * them after the update is successful to check for any bits + * changed. + */ + store_cpu_caps(&prev_info); + ret = stop_machine_cpuslocked(__reload_late, NULL, cpu_online_mask); if (ret == 0) microcode_check(&prev_info); -- 2.34.1
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