Re: [Xen-devel] run time memory trap question

[Andrii Tseglytskyi <andrii.tseglytskyi@xxxxxxxxxxxxxxx>]

Hi Julien,

>
>     > Can anyone clarify - is it possible to make a run time memory trap in
>     > Xen hypervisor?
>
>     I guess you are talking about ARM? If so, it's not possible right now.
>
>
> Does it mean, that it is possible on x86 ?

Yes, you can look at register_io_handler in xen/arch/x86/hvm/intercept.c

It's used a static array, but I don't think this is the solution for
ARM. We don't know in advance the maximum number of MMIO region to handle.

What I'm thinking about for ARM - is to use linked list for MMIO handlers + API to register / unregister handler.

xen/arch/arm/io.c:

 25 static const struct mmio_handler *const mmio_handlers[] =

 26 {   

 27     &vgic_distr_mmio_handler,

 28     &vuart_mmio_handler,

 29 };  

This can be changed to list. New API will add / remove entries. VGIC and VUART will call something like mmio_register_handler(&vgic_distr_mmio_handle) during corresponding initcall.

Than the only change which is required for existing int handle_mmio(mmio_info_t *info) function  - is to enumerate list, instead of array

 32 int handle_mmio(mmio_info_t *info)

 33 {

 34     struct vcpu *v = current;

 35     int i;

 36 

 37     for ( i = 0; i < MMIO_HANDLER_NR; i++ ) --> *list_for_each*

 38         if ( mmio_handlers[i]->check_handler(v, info->gpa) )

 39             return info->dabt.write ?

 40                 mmio_handlers[i]->write_handler(v, info) :

 41                 mmio_handlers[i]->read_handler(v, info);

 42 

 43     return 0;

 44 }

Something like this.

Regards,

Andrii

--
Julien Grall

--

Andrii Tseglytskyi | Embedded Dev
GlobalLogic
www.globallogic.com

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