Re: [RFC 02/37] s390/protvirt: introduce host side setup

[David Hildenbrand <david@redhat.com>]

On 24.10.19 15:25, David Hildenbrand wrote:
> On 24.10.19 13:40, Janosch Frank wrote:
>> From: Vasily Gorbik <gor@linux.ibm.com>
>>
>> Introduce KVM_S390_PROTECTED_VIRTUALIZATION_HOST kbuild option for
>> protected virtual machines hosting support code.
>>
>> Add "prot_virt" command line option which controls if the kernel
>> protected VMs support is enabled at runtime.
>>
>> Extend ultravisor info definitions and expose it via uv_info struct
>> filled in during startup.
>>
>> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
>> ---
>>    .../admin-guide/kernel-parameters.txt         |  5 ++
>>    arch/s390/boot/Makefile                       |  2 +-
>>    arch/s390/boot/uv.c                           | 20 +++++++-
>>    arch/s390/include/asm/uv.h                    | 46 ++++++++++++++++--
>>    arch/s390/kernel/Makefile                     |  1 +
>>    arch/s390/kernel/setup.c                      |  4 --
>>    arch/s390/kernel/uv.c                         | 48 +++++++++++++++++++
>>    arch/s390/kvm/Kconfig                         |  9 ++++
>>    8 files changed, 126 insertions(+), 9 deletions(-)
>>    create mode 100644 arch/s390/kernel/uv.c
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index c7ac2f3ac99f..aa22e36b3105 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -3693,6 +3693,11 @@
>>    			before loading.
>>    			See Documentation/admin-guide/blockdev/ramdisk.rst.
>>    
>> +	prot_virt=	[S390] enable hosting protected virtual machines
>> +			isolated from the hypervisor (if hardware supports
>> +			that).
>> +			Format: <bool>
> 
> Isn't that a virt driver detail that should come in via KVM module
> parameters? I don't see quite yet why this has to be a kernel parameter
> (that can be changed at runtime).
> 

I was confused by "runtime" in "which controls if the kernel protected 
VMs support is enabled at runtime"

So this can't be changed at runtime. Can you clarify why kvm can't 
initialize that when loaded and why we need a kernel parameter?

-- 

Thanks,

David / dhildenb