Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | From | Ashok Raj <> | Subject | [PATCH v3 2/2] x86/microcode/core: Take a snapshot before and after applying microcode | Date | Tue, 27 Dec 2022 13:01:44 -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.
microcode_store_cpu_caps() basically stores the original CPU reported values and not the OS modified values. This will avoid giving a false warning even if 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.
Fixes: 1008c52c09dc ("x86/CPU: Add a microcode loader callback") Signed-off-by: Ashok Raj <ashok.raj@intel.com> 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> --- Changes since last post
- Boris - Change function from copy_cpu_caps() -> store_cpu_caps() - 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 | 17 +++++++++++++++++ arch/x86/kernel/cpu/microcode/core.c | 7 +++++++ 3 files changed, 25 insertions(+)
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index 387578049de0..ac2e67156b9b 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -697,6 +697,7 @@ bool xen_set_default_idle(void); #endif void __noreturn stop_this_cpu(void *dummy); +void microcode_store_cpu_caps(struct cpuinfo_x86 *info); void microcode_check(struct cpuinfo_x86 *info); enum l1tf_mitigations { diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index b9c7529c920e..1f0b57a5d89d 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -2297,6 +2297,23 @@ void cpu_init_secondary(void) #endif #ifdef CONFIG_MICROCODE_LATE_LOADING + +void microcode_store_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 diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c index d86a4f910a6b..14d9031ed68a 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. + */ + microcode_store_cpu_caps(&info); + ret = stop_machine_cpuslocked(__reload_late, NULL, cpu_online_mask); if (ret == 0) microcode_check(&info); -- 2.34.1
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