Re: [Qemu-devel] Get host virtual address corresponding to guest physical address?

[Peter Maydell]

On 25 August 2012 14:17, 陳韋任 (Wei-Ren Chen) <address@hidden> wrote:
> On Sat, Aug 25, 2012 at 11:56:13AM +0100, Peter Maydell wrote:
>> On 24 August 2012 04:14, 陳韋任 (Wei-Ren Chen) <address@hidden> wrote:
>> >   I would like to know if there is a function in QEMU which converts
>> > a guest physical address into corresponding host virtual address.
>>
>> So the question is, what do you want to do with the host virtual
>> address when you've got it? cpu_physical_memory_map() is really intended
>> (as Blue says) for the case where you have a bit of host code that wants
>> to write a chunk of data and doesn't want to do a sequence of
>> cpu_physical_memory_read()/_write() calls. Instead you _map() the memory,
>> write to it and then _unmap() it.
>
>   We want to let host MMU hardware to do what softmmu does. As a prototype
> (x86 guest on x86_64 host), we want to do the following:
>
>   1. Get guest page table entries (GVA -> GPA).
>
>   2. Get corresponding HVA.
>
>   3. Then we use /dev/mem (with host cr3) to find out HPA.
>
>   4. We insert GVA -> HPA mapping into host page table through /dev/mem,
>      we already move QEMU above 4G to make way for the guest.

>   You mean if I call cpu_physical_memory_map with a guest MMIO (physcial)
> address, the first time it'll return the address of a buffer that I can write
> data into. The second time it'll return NULL since I don't call
> cpu_physical_memory_umap to flush the buffer. Do I understand you correctly?
> Hmm, I think we don't not have such issue in our use case... What do you
> think?

I think you would hit this when you tried to do this for a page of
guest memory which isn't RAM. In any case it's a sign that the API
is not the one you want.

-- PMM