Re: [Xen-devel] [PATCH v3 1/6] xen: do not initialize the interval timer emulator

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 27 Jan 2012, Jan Kiszka wrote:
> On 2012-01-27 19:21, Stefano Stabellini wrote:
> > PIT is emulated by the hypervisor so we don't need to emulate it in Qemu:
> > this patch prevents Qemu from waking up needlessly at PIT_FREQ on Xen.
> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > ---
> >  hw/pc.c |    7 +++++--
> >  1 files changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/hw/pc.c b/hw/pc.c
> > index 85304cf..7a7ce98 100644
> > --- a/hw/pc.c
> > +++ b/hw/pc.c
> > @@ -43,6 +43,7 @@
> >  #include "ui/qemu-spice.h"
> >  #include "memory.h"
> >  #include "exec-memory.h"
> > +#include "arch_init.h"
> >  
> >  /* output Bochs bios info messages */
> >  //#define DEBUG_BIOS
> > @@ -1130,7 +1131,7 @@ void pc_basic_device_init(ISABus *isa_bus, qemu_irq 
> > *gsi,
> >      DriveInfo *fd[MAX_FD];
> >      qemu_irq rtc_irq = NULL;
> >      qemu_irq *a20_line;
> > -    ISADevice *i8042, *port92, *vmmouse, *pit;
> > +    ISADevice *i8042, *port92, *vmmouse, *pit = NULL;
> >      qemu_irq *cpu_exit_irq;
> >  
> >      register_ioport_write(0x80, 1, 1, ioport80_write, NULL);
> > @@ -1151,7 +1152,9 @@ void pc_basic_device_init(ISABus *isa_bus, qemu_irq 
> > *gsi,
> >  
> >      qemu_register_boot_set(pc_boot_set, *rtc_state);
> >  
> > -    pit = pit_init(isa_bus, 0x40, 0);
> > +    if (!xen_available()) {
> > +        pit = pit_init(isa_bus, 0x40, 0);
> > +    }
> >      pcspk_init(pit);
> >  
> >      for(i = 0; i < MAX_SERIAL_PORTS; i++) {
> 
> Thus as guest accessing to port 0x61 will be able to crash qemu because
> pit is NULL? Or do you emulate that port in the kernel? If not, you
> likely want to move pcspk_init() under the same umbrella.

We already emulate both pit and port 0x61 in xen so a guest won't be
able to crash qemu that easily :)
But now that you make me think about it, it makes sense to move
pcspk_init under the same if, like you suggested.
Thanks,

Stefano

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