Re: [RFC 30/37] DOCUMENTATION: protvirt: Diag 308 IPL

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On 11/6/19 6:37 PM, Cornelia Huck wrote:
> On Wed, 6 Nov 2019 18:05:22 +0100
> Janosch Frank <frankja@xxxxxxxxxxxxx> wrote:
> 
>> On 11/6/19 5:48 PM, Cornelia Huck wrote:
>>> On Thu, 24 Oct 2019 07:40:52 -0400
>>> Janosch Frank <frankja@xxxxxxxxxxxxx> wrote:
>>>   
>>>> Description of changes that are necessary to move a KVM VM into
>>>> Protected Virtualization mode.
>>>>
>>>> Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
>>>> ---
>>>>  Documentation/virtual/kvm/s390-pv-boot.txt | 62 ++++++++++++++++++++++
>>>>  1 file changed, 62 insertions(+)
>>>>  create mode 100644 Documentation/virtual/kvm/s390-pv-boot.txt
> 
>>> So... what do we IPL from? Is there still a need for the bios?
>>>
>>> (Sorry, I'm a bit confused here.)
>>>   
>>
>> We load a blob via the bios (all methods are supported) and that blob
>> moves itself into protected mode. I.e. it has a small unprotected stub,
>> the rest is an encrypted kernel.
>>
> 
> Ok. The magic is in the loaded kernel, and we don't need modifications
> to the bios?
> 

Yes.

The order is:
* We load a blob via the bios or direct kernel boot.
* That blob consists of a small stub, a header and an encrypted blob
glued together
* The small stub does the diag 308 subcode 8 and 10.
* Subcode 8 basically passes the header that describes the encrypted
blob to the Ultravisor (well rather registers it with qemu to pass on later)
* Subcode 10 tells QEMU to move the VM into protected mode
* A lot of APIs in KVM and the Ultravisor are called
* The protected VM starts
* A memory mover copies the now unencrypted, but protected kernel to its
intended place and jumps into the entry function
* Linux boots and detects, that it is protected and needs to use bounce
buffers

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