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

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 02/17/2014 03:01 PM, Andrii Tseglytskyi wrote:
> 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.

This solution sounds good.

If I remembered correctly, you are writing a driver for IPU/GPU MMU, right?
In this case, I think a per-domain MMU handlers would be better. Most of
handlers will be used for a specific guest (except the VGIC handler).

-- 
Julien Grall

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