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

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Date: Fri, 17 May 2024 17:00:19 +0200
From: Jürgen Groß <jgross@...e.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: isaku.yamahata@...el.com, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
 Paolo Bonzini <pbonzini@...hat.com>, erdemaktas@...gle.com,
 Sean Christopherson <seanjc@...gle.com>, Sagi Shahar <sagis@...gle.com>,
 Kai Huang <kai.huang@...el.com>, chen.bo@...el.com, hang.yuan@...el.com,
 tina.zhang@...el.com, Xiaoyao Li <xiaoyao.li@...el.com>
Subject: Re: [PATCH v19 039/130] KVM: TDX: initialize VM with TDX specific
 parameters

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@...el.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