Commit 3ae6295c authored Jun 14, 2018 by Siarhei Liakh Committed by Thomas Gleixner Jun 20, 2018

x86: Call fixup_exception() before notify_die() in math_error()

fpu__drop() has an explicit fwait which under some conditions can trigger a
fixable FPU exception while in kernel. Thus, we should attempt to fixup the
exception first, and only call notify_die() if the fixup failed just like
in do_general_protection(). The original call sequence incorrectly triggers
KDB entry on debug kernels under particular FPU-intensive workloads.

Andy noted, that this makes the whole conditional irq enable thing even
more inconsistent, but fixing that it outside the scope of this.

Signed-off-by: Siarhei Liakh <siarhei.liakh@concurrent-rt.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Borislav Petkov" <bpetkov@suse.de>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/DM5PR11MB201156F1CAB2592B07C79A03B17D0@DM5PR11MB2011.namprd11.prod.outlook.com

parent 1d9f3e20

arch/x86/kernel/traps.c

+8 −6

Original line number	Diff line number	Diff line
		@@ -834,16 +834,18 @@ static void math_error(struct pt_regs *regs, int error_code, int trapnr)
		char *str = (trapnr == X86_TRAP_MF) ? "fpu exception" :
		"simd exception";

		if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, SIGFPE) == NOTIFY_STOP)
		return;
		cond_local_irq_enable(regs);

		if (!user_mode(regs)) {
		if (!fixup_exception(regs, trapnr)) {
		if (fixup_exception(regs, trapnr))
		return;

		task->thread.error_code = error_code;
		task->thread.trap_nr = trapnr;

		if (notify_die(DIE_TRAP, str, regs, error_code,
		trapnr, SIGFPE) != NOTIFY_STOP)
		die(str, regs, error_code);
		}
		return;
		}

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