Re: [PATCH v5 0/5] TDX host: kexec() support

["Huang, Kai" <kai.huang@intel.com>]

On 20/08/2024 10:28 am, Sagi Shahar wrote:
> On Mon, Aug 19, 2024 at 5:16 PM Huang, Kai <kai.huang@intel.com> wrote:
>>
>>
>>
>> On 20/08/2024 9:21 am, Sagi Shahar wrote:
>>>> Currently kexec() support and TDX host are muturally exclusive in the
>>>> Kconfig.  This series adds the TDX host kexec support so that they can
>>>> work together and can be enabled at the same time in the Kconfig.
>>>
>>> I tried testing the kexec functionality and noticed that the TDX module
>>> fails initialization on the second kernel so you can't actually kexec
>>> between 2 kernels that enable TDX. Is that the expected behavior? Are
>>> there future patches to enable that functionality?
>>>
>>
>> Thanks for testing!
>>
>> Yes this is the expected behaviour.  If the first kernel has enabled
>> TDX, then the second kernel will fail to init TDX.  The reason the first
>> SEAMCALL to initialize TDX module in the second kernel will fail due to
>> module having been initialized.
>>
>> However if the first kernel has not enabled TDX, the second kernel is
>> able to enable it.
> 
> Are there any plans to support both kernels being able to enable TDX
> in the future? Either by changes to KVM or the TDX module?

AFAICT we haven't received such requirement so far.  Let me double check 
internally and get back here.

Btw, if we want to do this purely from software, changing KVM isn't the 
right thing to do.  We need to somehow pass key data structures managing 
TDX module to the second kernel, e.g., module status, locations of 
PAMTs.  And the second kernel needs to be modified to understand those, 
which means some old (second) kernels with TDX support may not be able 
to support this even if we add this to the kernel.