4.17-stable review patch. If anyone has any objections, please let me know.
------------------
From: Siarhei Liakh Siarhei.Liakh@concurrent-rt.com
commit 3ae6295ccb7cf6d344908209701badbbbb503e40 upstream.
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@DM5PR11MB20... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kernel/traps.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-)
--- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -834,16 +834,18 @@ static void math_error(struct pt_regs *r 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)) { - task->thread.error_code = error_code; - task->thread.trap_nr = 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; }