Re: [Qemu-devel] [PATCH 03/16] tlb_set_page_with_attrs: Take argument specifying AddressSpace to use

[Peter Maydell]

On 9 November 2015 at 10:49, Peter Maydell <address@hidden> wrote:
> On 9 November 2015 at 10:44, Paolo Bonzini <address@hidden> wrote:
>>
>>
>> On 05/11/2015 19:15, Peter Maydell wrote:
>>> Add an argument to tlb_set_page_with_attrs which allows the target CPU code
>>> to tell the core code which AddressSpace to use.
>>>
>>> The AddressSpace is specified by the index into the array of ASes which
>>> were registered with cpu_address_space_init().
>>>
>>> Signed-off-by: Peter Maydell <address@hidden>
>>
>> Can it be deduced from the attributes instead?  Basically, you would have
>>
>>    int cpu_get_asidx(MemTxAttrs attrs);
>>
>> in cpu.h, which is called by tlb_set_page_with_attrs.
>> cpu_get_phys_page_asidx_debug could also be replaced by
>> cpu_get_phys_page_attrs_debug.
>
> For ARM it could, certainly (and as you say, if we go that
> way then some of the extra passing around of asidxes collapses,
> and in particular we don't need to keep them separately in the
> iotlb entries). I wasn't convinced that this would be true for
> all possible uses of AddressSpaces.

Having thought a bit more about this, I think you're right. At
any rate, our current planned multi-as use will certainly work
with the existing attrs. And we could always steal a few bits
in the MemTxAttrs to indicate the asidx for some hypothetical
future usage even if they wouldn't otherwise have to be
exposed to the rest of the system outside the CPU.

thanks
-- PMM