Re: [Qemu-devel] [RFC PATCH v1 15/22] i386: sev: register RAM read/write ops for BIOS and PC.RAM region

[Brijesh Singh]

On 09/14/2016 04:00 PM, Paolo Bonzini wrote:
> On 14/09/2016 22:59, Brijesh Singh wrote:
> > I will look into hooking up the callback into ROM read/write ops. I was
> > thinking about adding a new argument in
> > cpu_physical_memory_write_rom_internal()
> >
> > void cpu_physical_memory_write_rom(AddressSpace *as, hwaddr addr,
> >                                    const uint8_t *buf, int len,
> >                                    WriteCB *cb)
> > {
> >    ....
> >    ptr = qemu_map_ram_ptr(mr->ram_block, addr1);
> >
> >    if (cb)
> >      cb(ptr, buf, len)
> >    else
> >      memcpy(ptr, buf, len)
> > ....
> >
> > }
> >
> > In case of SEV, we pass a CB function pointer which calls SEV API's to
> > encrypt memory. Does this make sense?
>
> I think a global as you have it in this series is just fine---just don't
> hook it into address_space_read and address_space_write.

Actually in SEV RAM callback I check the Attrs, if attr.sev_debug flag 
set then use SEV debug command otherwise default to memcpy so that DMA 
and everything else works. I guest the main reason why i choose to hook 
this up in address_space_read/write was that I found that 
address_space_write and address_space_read is used in debug path. e.g

cpu_memory_rw_debug
  address_space_rw
    address_space_write/read

cpu_physical_memory_rw
 address_space_rw
   address_space_write/read

How do you want me to handle these cases? Having SEV RAM callback taking 
care this internally was my simplest solution,  I am certainly open to 
new ideas.