RE: How to get host virtual address from guest physical address?

[ckim]

Hello, Peter Maydell,

Thanks for the help.
I've seen that I can read the guest physical memory using 
cpu_physical_memory_read function.
I followed the function, but couldn't find a nicely cut 'guest physical to host 
virtual' address conversion function.
But I found I can do what I need (passing host virtual address to an .so file) 
using memory_region_get_ram_ptr function (keeping the return value and adding 
the offset from the start of known memory region to it).

This is for others why might get help from here : 
I passed the guest physical address to a register write function, and I can use 
the register value to access the guess memory like below.
        uint64_t membuf;
        cpu_physical_memory_read(guest_phys_addr, &membuf, 8);   // you need 
cache flush in the guest for this to work.
I've also seen that I can keep the start address (host virtual address seen 
from qemu) of a guest memory region like below after you do 
memory_region_init_ram().
         ram_ptr = memory_region_get_ram_ptr(my_memory_region);

Thank you!
Chan Kim

> -----Original Message-----
> From: Peter Maydell <peter.maydell@linaro.org>
> Sent: Friday, May 28, 2021 11:37 PM
> To: Chan Kim <ckim@etri.re.kr>
> Cc: qemu-discuss <qemu-discuss@nongnu.org>
> Subject: Re: How to get host virtual address from guest physical address?
> 
> On Fri, 28 May 2021 at 03:50, <ckim@etri.re.kr> wrote:
> > In my baremetal test on aarch64, I pass the guest physical address of an
> array of a structure to the qemu peripheral code using peripherals
> register.
> >
> > I soon realized the adderss is from another world and to access this
> address in qemu, I need the host virtual address.
> >
> > I tried reading the document (and will read more) but it shows the load
> and store APIs, and not the address translation API.
> >
> > I need that address because I have to pass the “address” to a function
> in a dynamic library ( a .so file). I don’t myself load or store using
> that address.
> >
> > What is the function for this “guest physical address to host virtual
> address” translation?
> 
> There is address_space_map(), but watch out for the caveats documented in
> its doc comment in memory.h.
> 
> thanks
> -- PMM