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From: Brijesh Singh <brijesh.singh@amd.com>
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Date: Wed, 14 Sep 2016 15:59:34 -0500
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Subject: Re: [Qemu-devel] [RFC PATCH v1 15/22] i386: sev: register RAM
 read/write ops for BIOS and PC.RAM region
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To: Paolo Bonzini <pbonzini@redhat.com>, ehabkost@redhat.com, crosthwaite.peter@gmail.com, armbru@redhat.com, mst@redhat.com, p.fedin@samsung.com, qemu-devel@nongnu.org, lcapitulino@redhat.com, rth@twiddle.net
Cc: brijesh.singh@amd.com

Hi Paolo,

On 09/13/2016 06:05 PM, Paolo Bonzini wrote:
>
>
> On 13/09/2016 16:49, Brijesh Singh wrote:
>>
>> +    /* Register SEV read/write ops for the guest RAM */
>> +    if (kvm_sev_enabled())
>> +        memory_region_set_ram_ops(ram, kvm_sev_get_ram_ops());
>
> If you don't actually need this one except for -kernel it would be very
> nice, because then the hooks could be limited to cpu_memory_rw_debug.
>

Yes so far i see that we needing this only for -kernel option.

> address_space_write and address_space_read are the central entry point
> for device DMA, and calling mr->ram_ops->write from there seems very
> wrong.  I'd rather make those hooks *ROM* read/write ops rather than RAM
> read/write ops.
>

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?

-Brijesh