Commit-ID: ed68d7e9b9cfb64f3045ffbcb108df03c09a0f98
Gitweb: http://git.kernel.org/tip/ed68d7e9b9cfb64f3045ffbcb108df03c09a0f98
Author: Andy Lutomirski <[email protected]>
AuthorDate: Sat, 19 Nov 2016 15:37:30 -0800
Committer: Ingo Molnar <[email protected]>
CommitDate: Mon, 21 Nov 2016 09:04:32 +0100
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 <[email protected]>
Signed-off-by: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link:
http://lkml.kernel.org/r/70eac6639f23df8be5fe03fa1984aedd5d40077a.1479598603.git.l...@kernel.org
Signed-off-by: Ingo Molnar <[email protected]>
---
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 26240dd..4224ede 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");
