Re: [PATCH v19 039/130] KVM: TDX: initialize VM with TDX specific parameters

Jürgen Groß
2024-05-17T15:00:21Z

On 17.05.24 16:53, Kirill A. Shutemov wrote:
> On Fri, May 17, 2024 at 04:37:16PM +0200, Juergen Gross wrote:
>> On 17.05.24 16:32, Kirill A. Shutemov wrote:
>>> On Mon, Feb 26, 2024 at 12:25:41AM -0800, isaku.yamahata@intel.com wrote:
>>>> @@ -725,6 +967,17 @@ static int __init tdx_module_setup(void)
>>>> tdx_info->nr_tdcs_pages = tdcs_base_size / PAGE_SIZE;
>>>> + /*
>>>> + * Make TDH.VP.ENTER preserve RBP so that the stack unwinder
>>>> + * always work around it. Query the feature.
>>>> + */
>>>> + if (!(tdx_info->features0 & MD_FIELD_ID_FEATURES0_NO_RBP_MOD) &&
>>>> + !IS_ENABLED(CONFIG_FRAME_POINTER)) {
>>>
>>> I think it supposed to be IS_ENABLED(CONFIG_FRAME_POINTER). "!" shouldn't
>>> be here.
>>
>> No, I don't think so.
>>
>> With CONFIG_FRAME_POINTER %rbp is being saved and restored, so there is no
>> problem in case the seamcall is clobbering it.
>
> Could you check setup_tdparams() in your tree?
>
> Commit
>
> [SEAM-WORKAROUND] KVM: TDX: Don't use NO_RBP_MOD for backward compatibility
>
> in my tree comments out the setting TDX_CONTROL_FLAG_NO_RBP_MOD.
>
> I now remember there was problem in EDK2 using RBP. So the patch is
> temporary until EDK2 is fixed.
>

I have the following line in setup_tdparams() (not commented out):

td_params->exec_controls = TDX_CONTROL_FLAG_NO_RBP_MOD;

Juergen