From ed68d7e9b9cfb64f3045ffbcb108df03c09a0f98 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Sat, 19 Nov 2016 15:37:30 -0800 Subject: [PATCH] x86/boot: Fail the boot if !M486 and CPUID is missing Linux will have all kinds of sporadic problems on systems that don't have the CPUID instruction unless CONFIG_M486=y. In particular, sync_core() will explode. I believe that these kernels had a better chance of working before commit 05fb3c199bb0 ("x86/boot: Initialize FPU and X86_FEATURE_ALWAYS even if we don't have CPUID"). That commit inadvertently fixed a serious bug: we used to fail to detect the FPU if CPUID wasn't present. Because we also used to forget to set X86_FEATURE_ALWAYS, we end up with no cpu feature bits set at all. This meant that alternative patching didn't do anything and, if paravirt was disabled, we could plausibly finish the entire boot process without calling sync_core(). Rather than trying to work around these issues, just have the kernel fail loudly if it's running on a CPUID-less 486, doesn't have CPUID, and doesn't have CONFIG_M486 set. Reported-by: Matthew Whitehead Signed-off-by: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/70eac6639f23df8be5fe03fa1984aedd5d40077a.1479598603.git.luto@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/boot/cpu.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/arch/x86/boot/cpu.c b/arch/x86/boot/cpu.c index 26240dde081e..4224ede43b4e 100644 --- a/arch/x86/boot/cpu.c +++ b/arch/x86/boot/cpu.c @@ -87,6 +87,12 @@ int validate_cpu(void) return -1; } + if (CONFIG_X86_MINIMUM_CPU_FAMILY <= 4 && !IS_ENABLED(CONFIG_M486) && + !has_eflag(X86_EFLAGS_ID)) { + printf("This kernel requires a CPU with the CPUID instruction. Build with CONFIG_M486=y to run on this CPU.\n"); + return -1; + } + if (err_flags) { puts("This kernel requires the following features " "not present on the CPU:\n"); -- 2.20.1