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

[Jan Kiszka]

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 <address@hidden>
> ---
>  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.

Jan

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