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

[Janosch Frank <frankja@linux.ibm.com>]

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On 11/7/19 9:53 AM, Cornelia Huck wrote:
> On Wed, 6 Nov 2019 22:02:41 +0100
> Janosch Frank <frankja@linux.ibm.com> wrote:
> 
>> On 11/6/19 6:37 PM, Cornelia Huck wrote:
>>> On Wed, 6 Nov 2019 18:05:22 +0100
>>> Janosch Frank <frankja@linux.ibm.com> wrote:
>>>   
>>>> On 11/6/19 5:48 PM, Cornelia Huck wrote:  
>>>>> On Thu, 24 Oct 2019 07:40:52 -0400
>>>>> Janosch Frank <frankja@linux.ibm.com> wrote:
>>>>>     
>>>>>> Description of changes that are necessary to move a KVM VM into
>>>>>> Protected Virtualization mode.
>>>>>>
>>>>>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>>>>>> ---
>>>>>>  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
>>
> 
> Thanks, this explanation makes things much clearer.

NP
We seem to assume that all of this is easily understandable, but we are
obviously biased :-)
I'll try to improve Documentation by adding Pierre to the discussion, as
he wasn't involved in the project yet.



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