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authorAndy Lutomirski <luto@kernel.org>2016-11-19 15:37:30 -0800
committerIngo Molnar <mingo@kernel.org>2016-11-21 09:04:32 +0100
commited68d7e9b9cfb64f3045ffbcb108df03c09a0f98 (patch)
tree8074e77929a016279e03e5fd75252b0e6ab654b6 /arch/x86
parentfc0e81b2bea0ebceb71889b61d2240856141c9ee (diff)
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 <tedheadster@gmail.com> Signed-off-by: Andy Lutomirski <luto@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/70eac6639f23df8be5fe03fa1984aedd5d40077a.1479598603.git.luto@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/boot/cpu.c6
1 files changed, 6 insertions, 0 deletions
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");