Re: [RFC v4 06/13] OvmfPkg:AmdSevDxe: add AmdSevDxe driver

[Brijesh Singh <brijesh.singh@amd.com>]

Hi Jordan,

On 5/15/17 12:47 PM, Jordan Justen wrote:
> On 2017-05-11 11:01:57, Brijesh Singh wrote:
>>
>> We basically need some kind of guarantee that this driver is run before any other
>> drivers or libs access MMIO register/buffers. In additional to clearing encryption
>> bit from MMIO spaces, the driver also installs IOMMU protocol. So far, IOMMU protocol
>> is directly consumed by PciHostBridgeDxe driver and QemuFwCfgDxeLib.
> What about adding a NULL protocol named
> gOvmfIoMmuDetectionProtocolGuid? (Better name suggestions welcomed. :)
> Then we can use this protocol in a depex where needed.
It should be doable, If I find better name then I will use that :)
> Maybe we should consider naming the driver IoMmuDxe instead?
>
> I think the generic PciRoot bridge driver shouldn't need this in the
> depex because it will not start until the BDS phase, and the IoMmuDxe
> driver would have been dispatched by then.
Are you suggesting that we introduce a new IoMmuDxe driver and install
IOMMU protocol unconditionally ? I was hoping that we install IOMMU
protocol only when SEV is enabled. A non-SEV guest will still use the
old approach.  I was minimizing changes into non-SEV code flow.  Please
note that since AmdSevDxe driver does *two* things; a) clear C-bit from
MMIO b) installs IOMMU protocol hence I will not able to remove 
AmdSevDxe completely.  But I can remove IOMMU protocol installation part
from AmdSevDxe and move it into new IoMmuDxe driver.  Please let me know
if this is what you are asking.  thanks

-Brijesh