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

[Paolo Bonzini]

On 14/09/2016 23:47, Brijesh Singh wrote:
> 
> 
> 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

Right, but if you change this to a ROM hook only, cpu_memory_rw_debug
will go through cpu_physical_memory_write_rom instead.  This will invoke
the hook properly, won't it?  It will break -kernel unless fw_cfg DMA is
disabled, of course.

Paolo