Re: [Qemu-devel] [PATCH] rtc: introduce nmi disable bit handler for cmos

[Gonglei (Arei)]

> -----Original Message-----
> From: Eduardo Habkost [mailto:address@hidden
> Sent: Tuesday, December 15, 2015 2:17 AM
> To: Gonglei (Arei)
> Cc: address@hidden; address@hidden; address@hidden;
> address@hidden; Huangpeng (Peter)
> Subject: Re: [PATCH] rtc: introduce nmi disable bit handler for cmos
> 
> On Sat, Dec 12, 2015 at 09:15:46PM +0800, Gonglei wrote:
> > The Non-Maskable Interrupt (NMI) Enable bit is 0x80 bit of Port 0x70
> > (and its aliases). This bit must be 0b to enable the hardware chipset
> > to send a Non-Maskable Interrupt. When set to a 1b, NMI's are
> > disabled. This bit is commonly accessed by applications, BIOS, and
> > even the operating system since it is used to block NMI assertions
> > when sensitive code is executing.
> >
> > Currently, QEMU do no not handle the bit, means Qemu cannot block NMI
> > occur, sometimes maybe cause a race between the CMOS read/write and
> > the NMI handler. If you are setting the CMOS clock or reading CMOS RAM
> > and an NMI occurs, Bad values could be written to or read from the
> > CMOS RAM, or the NMI operation might not occur correctly.
> >
> > This patch introduce nmi disable bit handler to fix the problem and
> > make the emulated CMOS like the real hardware.
> >
> > Signed-off-by: Gonglei <address@hidden>
> > ---
> >  Please refer to:
> >    https://lists.gnu.org/archive/html/qemu-devel/2015-11/msg00616.html
> >
> >  Note: We can't reproduce the problem, what a pity :(  I holp the
> > patch can fix it. Please review, thanks!
> > ---
> >  hw/i386/kvm/apic.c                  |  4 +++-
> >  hw/timer/mc146818rtc.c              | 11 +++++++++++
> >  include/hw/timer/mc146818rtc_regs.h |  3 +++
> >  include/sysemu/sysemu.h             |  1 +
> >  target-i386/kvm.c                   |  4 ++--
> >  vl.c                                |  1 +
> >  6 files changed, 21 insertions(+), 3 deletions(-)
> >
> [...]
> > diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h index
> > 3bb8897..a5b2342 100644
> > --- a/include/sysemu/sysemu.h
> > +++ b/include/sysemu/sysemu.h
> > @@ -177,6 +177,7 @@ extern uint8_t qemu_extra_params_fw[2];  extern
> > QEMUClockType rtc_clock;  extern const char *mem_path;  extern int
> > mem_prealloc;
> > +extern bool nmi_disabled;
> 
> Please, not another global variable. Doesn't this belong to struct RTCState or
> APICCommonState?
> 
OK, I'll think about changing this in the next version, thanks.


Regards,
-Gonglei