From cda64169bade79427f264e43d0f422eaed9dc116 Mon Sep 17 00:00:00 2001 From: Borislav Petkov Date: Wed, 13 May 2026 22:06:01 +0200 Subject: x86/microcode: Do not access MSR_IA32_PLATFORM_ID when running as a guest Patch in Fixes: causes the usual: unchecked MSR access error: RDMSR from 0x17 at ... (intel_get_platform_id) Call Trace: early_init_intel early_cpu_init setup_arch _printk start_kernel x86_64_start_reservations x86_64_start_kernel common_startup_64 because the kernel is booted in a guest. In order to avoid it, this MSR access needs to be prevented when running virtualized. That is usually done by checking X86_FEATURE_HYPERVISOR but for this particular case it is too early yet. The platform ID needs to be read as early as when microcode is loaded on the BSP: load_ucode_bsp ... -> get_microcode_blob ... -> intel_find_matching_signature and by that time, CPUID leafs haven't been parsed yet. The microcode loader already has logic to check early whether the kernel is running virtualized so make that globally available to arch/x86/. The query whether running virtualized is getting more and more prominent in recent times so might as well make it an arch-global var which the rest of the code can use. Fixes: d8630b67ca1ed ("x86/cpu: Add platform ID to CPU info structure") Reported-by: Vishal Verma Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Binbin Wu Reviewed-by: Xiaoyao Li Tested-by: Binbin Wu Link: https://lore.kernel.org/all/20260430020953.1405535-1-binbin.wu@linux.intel.com --- arch/x86/kernel/cpu/microcode/intel.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'arch/x86/kernel/cpu/microcode/intel.c') diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c index 37ac4afe0972..a4c0a0cf928b 100644 --- a/arch/x86/kernel/cpu/microcode/intel.c +++ b/arch/x86/kernel/cpu/microcode/intel.c @@ -138,6 +138,9 @@ u32 intel_get_platform_id(void) { unsigned int val[2]; + if (x86_hypervisor_present) + return 0; + /* * This can be called early. Use CPUID directly instead of * relying on cpuinfo_x86 which may not be fully initialized. -- cgit v1.2.3