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Re: [Qemu-devel] About address mapping between host and guest in QEMU


From: Wenjie Liu
Subject: Re: [Qemu-devel] About address mapping between host and guest in QEMU
Date: Wed, 22 Apr 2015 23:26:49 +0800

In http://vm-kernel.org/blog/2009/07/10/qemu-internal-part-2-softmmu/, the following equation is mentioned.
host_virtual_address = phys_ram_base(qemu variable) + guest_physical_address – guest_physical_address_base(0 in MIPS)

I think I have got the phys_ram_base and guest_physical_address, but can anybody tell me what is guest_physical_address_base?
I saw the memory allocation part in qemu/pc/pc.c:

    /* allocate RAM */
    ram_addr = qemu_ram_alloc(NULL, "pc.ram",
                              below_4g_mem_size + above_4g_mem_size);
    cpu_register_physical_memory(0, 0xa0000, ram_addr);
    cpu_register_physical_memory(0x100000,
                 below_4g_mem_size - 0x100000,
                 ram_addr + 0x100000);
#if TARGET_PHYS_ADDR_BITS > 32
    if (above_4g_mem_size > 0) {
        cpu_register_physical_memory(0x100000000ULL, above_4g_mem_size,
                                     ram_addr + below_4g_mem_size);
    }
#endif

I think the 0x100000, 0xa0000 and 0x100000000ULL have some relation with the guest_physical_address_base.

Is that so?



2015-04-22 21:31 GMT+08:00 Wenjie Liu <address@hidden>:
Hi all,
I have a little problem about the address mapping between host and guest in QEMU.

I have got the guest physical address and the host virtual base address of guest's memory space which by check the ramblocks list.

So, can I access to the guest's memory content by simply add the guest physical address with the base?

For example, if the guest physical address of a guest memory request is 0x000000011f9ff000, and the host virtual base is 0x00007f37ef122000, I am going to access the host virtual address 0x000000011f9ff000 + 0x00007f37ef122000.
Is this correct?


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Best regards




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Wenjie Liu

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E-mail: address@hidden

Wuhan National Laboratory for Optoelectronics,

Huazhong University of Science&Technology,

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