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Date: Fri, 11 Nov 2011 16:11:56 +0000
Message-ID: <CAFEAcA8DMx-e5iBqiC3eLu87TNG8hON3QrZ3t0-VCJd0U18Qgg@mail.gmail.com>
From: Peter Maydell <peter.maydell@linaro.org>
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Subject: Re: [Qemu-devel] [PATCH] s390x: initialize virtio dev region
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To: Alexander Graf <agraf@suse.de>
Cc: qemu-devel@nongnu.org

On 11 November 2011 15:59, Alexander Graf <agraf@suse.de> wrote:
> This is the machine init function. The s390 virtio machine's ram layout i=
s
> defined to be exactly as I posted in the previous post. So there won't be
> any ram starts at !=3D 0 or multiple mappings :).

That's the layout of the RAM in target_phys_addr_t space.
The layout of the ram in ram_addr_t space is not guaranteed
to be the same, it just happens to be in this case.

>>> On 10.11.2011, at 02:36, Peter Maydell wrote:
>> In summary, either:
>> (1) you need to ask the memory region for its ram_addr_t
>> [there doesn't seem to be an API for this at the moment],
>> do arithmetic on ram_addr_t's and use qemu_get_ram_ptr() to
>> get a host pointer corresponding to that ram_addr_t
>> or (2) you need to do your arithmetic in target_phys_addr_t's
>> (and then you can say your RAM starts at physaddr 0, which
>> is guaranteed, rather than at ram_addr_t 0, which isn't)
>> and use cpu_physical_memory_map/unmap().
>
> I still don't get it. What I want is:
>
> =C2=A0for (i =3D ram_size; i < my_ram_size; i++)
> =C2=A0 =C2=A0stb_phys(env, i, 0);
>
> cpu_physical_memory_map gives me a pointer to the memory region between
> ram_size and my_ram_size. I memset(0) it. I don't see how I could possibl=
y
> have different offsets anywhere. If cpu_physical_memory_map would take
> anything different than physical address, a lot of assumptions in QEMU co=
de
> would break.

Yes, so that's option (2) and you need to be using a target_phys_addr_t.

-- PMM