[okl4-developer] About the virtual memory management of OKL4

[Ben Leslie]

On Sun Nov 25, 2007 at 17:21:09 +0800, kashin Lin wrote:
>Hi,
>
>thanks for your reply, i got more clear about that.
>
>i still have some quetions:
>
>as you mentioned last time :" Any other address spaces have their mappings
>initialised by the
>root task itself", are those mappings for "RAM memory
>space"  only? because i noticed that some
>codes (like driver) call "hardware_back_memsection(memory, PHY_BASE,
>L4_IOMemory)" first
>before they can access those "IO memory space".

No, they can be for anything in the physical memory
address space, whether that is RAM, or device registers or
something else.

>if i write a l4 application (ex: in
>okl4_src/iguana/example/), which wants to access DSP memory.
>should i call "hardware_back_memsection" first ? for example:
>                uint32_t dsp_virt;
>                uintptr_t dsp_obj;
>
>                dsp_obj = memsection_create_user(0x1000, &dsp_virt);
>                hardware_back_memsection(dsp_obj, DSP_BASE, L4_IOMemory);
>
>                and use **(dsp_virt + offset) to access DSP?
>or i can just use *DSP_BASE to access it?

This would be the way to go.

Cheers,

Ben

>
>best regards,
>
>kashin lin
>
>
>2007/11/21, Ben Leslie <benno at ok-labs.com>:
>>
>> On Sat Nov 17, 2007 at 18:19:52 +0800, kashin Lin wrote:
>> >Hi,
>> >
>> >i have read okl4-progmanual & iguana-usermanual, but confused their
>> memory
>> >management.
>> >
>> >in l4 microkernel, threads in the same address space belong to the same
>> >process(task). so it means
>> >there will be various address
>> >space. but with iguana, all threads belong to the same process(task) are
>> >in the same
>> >address space with different PD. all thread created by iguana are also
>> >l4 threads ,
>> >why those difference exist?
>>
>> How the microkernel and the root task relate is a confusing point of
>> L4.
>>
>> The root task, in this case Iguana, is free to present its own
>> abstraction to user programs. It uses the underlying microkernel to
>> implement those abstractions.
>>
>> In this case, each Iguana protection domain is implemented by an
>> underlying L4 address space.
>>
>> It happens that Iguana ensures that all these L4 address spaces have
>> the same virtual -> physical mapping. (Although they do have different
>> permissions on the virtual memory.)
>>
>>
>> >in l4 microkernel, threads can communicatin between different or same  AS
>> by
>> >l4_IPC. but
>> >according to iguana manual, why it says "Explicit L4 mapping IPC is not
>> >permitted between Iguana
>> >protection domains". threads created with iguana are in the same AS,
>> aren't
>> >they?
>>
>> This is a case of the usermanuals being slightly out of date. Older
>> versions of the L4 API allowed memory to be mapped between L4 address
>> space by sending a "mapping IPC". To ensure the single-address-space
>> model is preserved, Iguana did not allow this operation to occur.
>>
>> The latest versions of L4 do not have this feature any more, so the
>> comment
>> in the Iguana manual is redundant.
>>
>> >if i created a thread, what's are the address space it can access (PHY
>> >addr)?
>> >either creating a thread "directly on L4" or "with iguana", will the
>> >PHY address
>> >it can access be different?
>>
>> In L4 the only way to create a thread is have the root-task create it.
>> So, if you are using Iguana, only Iguana is allowed to directly create
>> a thread. Any other programs that wish to create threads must ask
>> Iguana to do this on their behalf.
>>
>> >(in okl4-progmanual, it says "This address space is initialised at boot
>> time
>> >by the microkernel based
>> >on the initial mapping descriptors in the KIP memory descriptors as
>> >described in Chapter B-5."
>> >but it's missing)
>>
>> This refers to the address initial root task address space. Any other
>> address spaces have their mappings initialised by the root task itself.
>>
>> >maybe these quetions due
>> >to my less comprehend of the relationship between l4 & iguana.
>> >so it will be better if you can show me that.
>> >
>> >i really need to comprehend those. any help will be welcome!
>> >thanks in advance~
>>
>> Hopefully this has helped explain things, but maybe not. If not please
>> feel free to write again, and I will try to clarify any points.
>>
>> Cheers,
>>
>> Benno
>>