Messages in this thread Patch in this message | | | From | Ashok Raj <> | Subject | [PATCH v2 2/6] x86/microcode/core: Take a snapshot before and after applying microcode | Date | Tue, 27 Dec 2022 11:23:36 -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 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() - Thomas : Commit log changes. --- arch/x86/kernel/cpu/microcode/core.c | 42 +++++++++++++++++++++------- 1 file changed, 32 insertions(+), 10 deletions(-)
diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c index 0051ebf7c53e..e2cdf3e989e7 100644 --- a/arch/x86/kernel/cpu/microcode/core.c +++ b/arch/x86/kernel/cpu/microcode/core.c @@ -432,12 +432,28 @@ static int __reload_late(void *info) return ret; } +static void 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 * hotplug lock. */ -static void microcode_check(void) +static void microcode_check(struct cpuinfo_x86 *orig) { struct cpuinfo_x86 info; @@ -447,15 +463,13 @@ 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(). + */ + store_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; @@ -470,6 +484,7 @@ 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"); @@ -477,9 +492,16 @@ 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(&info); + ret = stop_machine_cpuslocked(__reload_late, NULL, cpu_online_mask); if (ret == 0) - microcode_check(); + microcode_check(&info); pr_info("Reload completed, microcode revision: 0x%x -> 0x%x\n", old, boot_cpu_data.microcode); -- 2.34.1
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