linux-kernel - Re: [PATCH 1/2] powerpc/prom_init: Replace linux,sml-base/sml-size with linux,sml-log

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Message-ID: <851536a5-ad8f-4d65-8c33-707e2fe762df@linux.ibm.com>
Date: Fri, 8 Mar 2024 07:23:35 -0500
From: Stefan Berger <stefanb@...ux.ibm.com>
To: Rob Herring <robh@...nel.org>, Michael Ellerman <mpe@...erman.id.au>
Cc: linux-integrity@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, jarkko@...nel.org,
        rnsastry@...ux.ibm.com, peterhuewe@....de, viparash@...ibm.com
Subject: Re: [PATCH 1/2] powerpc/prom_init: Replace linux,sml-base/sml-size
 with linux,sml-log



On 3/7/24 16:52, Rob Herring wrote:
> On Thu, Mar 07, 2024 at 09:41:31PM +1100, Michael Ellerman wrote:
>> Stefan Berger <stefanb@...ux.ibm.com> writes:
>>> linux,sml-base holds the address of a buffer with the TPM log. This
>>> buffer may become invalid after a kexec and therefore embed the whole TPM
>>> log in linux,sml-log. This helps to protect the log since it is properly
>>> carried across a kexec with both of the kexec syscalls.
>>>
>>> Signed-off-by: Stefan Berger <stefanb@...ux.ibm.com>
>>> ---
>>>   arch/powerpc/kernel/prom_init.c | 8 ++------
>>>   1 file changed, 2 insertions(+), 6 deletions(-)
>>>

> 
> 
>> Also adding the new linux,sml-log property should be accompanied by a
>> change to the device tree binding.
>>
>> The syntax is not very obvious to me, but possibly something like?
>>
>> diff --git a/Documentation/devicetree/bindings/tpm/ibm,vtpm.yaml b/Documentation/devicetree/bindings/tpm/ibm,vtpm.yaml
>> index 50a3fd31241c..cd75037948bc 100644
>> --- a/Documentation/devicetree/bindings/tpm/ibm,vtpm.yaml
>> +++ b/Documentation/devicetree/bindings/tpm/ibm,vtpm.yaml
>> @@ -74,8 +74,6 @@ required:
>>     - ibm,my-dma-window
>>     - ibm,my-drc-index
>>     - ibm,loc-code
>> -  - linux,sml-base
>> -  - linux,sml-size
> 
> Dropping required properties is an ABI break. If you drop them, an older
> OS version won't work.

1) On PowerVM and KVM on Power these two properties were added in the 
Linux code. I replaced the creation of these properties with creation of 
linux,sml-log (1/2 in this series). I also replaced the handling of
these two (2/2 in this series) for these two platforms but leaving it 
for powernv systems where the firmware creates these.

https://elixir.bootlin.com/linux/latest/source/arch/powerpc/kernel/prom_init.c#L1959

2) There is an example in the ibm,vtpm.yaml file that has both of these
and the test case still passes the check when the two entries above are 
removed. I will post v2 with the changes to the DT bindings for 
linux,sml-log including an example for linux,sml-log. [The test cases 
fail, as expected, when an additional property is added, such as when 
linux,sml-base is added when linux,sml-log is there or linux,sml-log is 
added when linux,sml-base is there.]

> 
>>   
>>   allOf:
>>     - $ref: tpm-common.yaml#
>> diff --git a/Documentation/devicetree/bindings/tpm/tpm-common.yaml b/Documentation/devicetree/bindings/tpm/tpm-common.yaml
>> index 3c1241b2a43f..616604707c95 100644
>> --- a/Documentation/devicetree/bindings/tpm/tpm-common.yaml
>> +++ b/Documentation/devicetree/bindings/tpm/tpm-common.yaml
>> @@ -25,6 +25,11 @@ properties:
>>         base address of reserved memory allocated for firmware event log
>>       $ref: /schemas/types.yaml#/definitions/uint64
>>   
>> +  linux,sml-log:
> 
> Why is this Linux specific?

I am not sure about the criteria when to prefix with 'linux,' and when 
not to. In this case I did it because it is created by Linux and because 
of existing linux,sml-base and linux,sml-size.