Messages in this thread |  | | | Date | Wed, 20 Oct 2010 12:03:16 +0200 | | From | Robert Richter <> | | Subject | Re: [PATCH 4/5] x86, NMI: Allow NMI reason io port (0x61) to be processed on any CPU |
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On 19.10.10 20:23:12, Huang Ying wrote: > On Wed, 2010-10-20 at 02:37 +0800, Don Zickus wrote: > > On Tue, Oct 19, 2010 at 06:25:07PM +0200, Robert Richter wrote: > > > On 19.10.10 17:07:01, Robert Richter wrote: > > > > On 15.10.10 22:22:17, Don Zickus wrote: > > > > > From: Huang Ying <ying.huang@intel.com> > > > > > > > > > > In original NMI handler, NMI reason io port (0x61) is only processed > > > > > on BSP. This makes it impossible to hot-remove BSP. To solve the > > > > > issue, a raw spinlock is used to make the port can be processed on any > > > > > CPU. > > > > > > > > > > Signed-off-by: Huang Ying <ying.huang@intel.com> > > > > > Signed-off-by: Don Zickus <dzickus@redhat.com> > > > > > --- > > > > > arch/x86/kernel/traps.c | 45 +++++++++++++++++++++++++-------------------- > > > > > 1 files changed, 25 insertions(+), 20 deletions(-) > > > > > > > > @@ -400,28 +405,28 @@ static notrace __kprobes void default_do_nmi(struct pt_regs *regs) > > > > > return; > > > > > > > > > > /* Non-CPU-specific NMI: NMI sources can be processed on any CPU */ > > > > > - cpu = smp_processor_id(); > > > > > - /* Only the BSP gets external NMIs from the system. */ > > > > > - if (!cpu) { > > > > > - reason = get_nmi_reason(); > > > > > - if (reason & NMI_REASON_MASK) { > > > > > - if (notify_die(DIE_NMI, "nmi", regs, reason, 2, SIGINT) > > > > > - == NOTIFY_STOP) > > > > > - return; > > > > > - if (reason & NMI_REASON_SERR) > > > > > - pci_serr_error(reason, regs); > > > > > - else if (reason & NMI_REASON_IOCHK) > > > > > - io_check_error(reason, regs); > > > > > + raw_spin_lock(&nmi_reason_lock); > > > > > > > > What about using raw_spin_trylock() instead? We don't have to wait > > > > here since we are already processing it by another cpu. > > > > > > This would avoid a global lock and also deadlocking in case of a > > > potential #gp in the nmi handler. > > > > I would feel more comfortable with it too. I can't find a reason where > > trylock would do harm. > > One possible issue can be as follow: > > - PCI SERR NMI raised on CPU 0 > - IOCHK NMI raised on CPU 1 > > If we use try lock, we may get unknown NMI on one CPU. Do you guys think > so?
This could be a valid point. On the other side the former implementation to let only handle cpu #0 i/o interrupts didn't trigger unknown nmis, so try_lock wouldn't change much compared to this. To be sure we might do a NOTIFY_STOP in the unknown path if we don't get the lock.
-Robert
-- Advanced Micro Devices, Inc. Operating System Research Center
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