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

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Date: Fri, 24 May 2024 11:37:15 +1200
From: "Huang, Kai" <kai.huang@...el.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Jürgen Groß <jgross@...e.com>
CC: "Yamahata, Isaku" <isaku.yamahata@...el.com>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "isaku.yamahata@...il.com"
	<isaku.yamahata@...il.com>, Paolo Bonzini <pbonzini@...hat.com>, "Aktas,
 Erdem" <erdemaktas@...gle.com>, Sean Christopherson <seanjc@...gle.com>,
	"Sagi Shahar" <sagis@...gle.com>, "Chen, Bo2" <chen.bo@...el.com>, "Yuan,
 Hang" <hang.yuan@...el.com>, "Zhang, Tina" <tina.zhang@...el.com>, "Li,
 Xiaoyao" <Xiaoyao.Li@...el.com>
Subject: Re: [PATCH v19 039/130] KVM: TDX: initialize VM with TDX specific
 parameters



On 18/05/2024 4:25 am, Kirill A. Shutemov wrote:
> On Fri, May 17, 2024 at 05:00:19PM +0200, Jürgen Groß wrote:
>> 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;
> 
> Could you check if it is visible from the guest side?
> 
> It is zero for me.
> 
> diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
> index c1cb90369915..f65993a6066d 100644
> --- a/arch/x86/coco/tdx/tdx.c
> +++ b/arch/x86/coco/tdx/tdx.c
> @@ -822,13 +822,33 @@ static bool tdx_enc_status_change_finish(unsigned long vaddr, int numpages,
>   	return true;
>   }
>   
> +#define TDG_VM_RD			7
> +
> +#define TDCS_CONFIG_FLAGS		0x1110000300000016
> +

Hi Kirill,

Where did you get this metadata field ID value from?  I assume you meant 
below one, from which the ID is 0x9110000300000016?

Or is there anything special rule for using metadata field ID in the guest?

     {
       "Control Structure": "TDCS",
       "Class": "Execution Controls",
       "Field Name": "CONFIG_FLAGS",
       "Description": [
         "Non-attested TD configuration flags"
       ],
       "Type": "64b bitmap",
       "VM Applicability": null,
       "Mutability": "TDH.MNG.INIT/  TDH.IMPORT.STATE.IMMUTABLE",
       "Initial Value": "From TDH.MNG.INIT input",
       "Field Size (Bytes)": "8",
       "Num Fields": "1",
       "Num Elements": "1",
       "Element Size (Bytes)": "8",
       "Overall Size (Bytes)": "8",
       "Base FIELD_ID (Hex)": "0x9110000300000016",
       "Host VMM Access for a Production TD": "RO",
       "Host VMM Access for a Debug TD": "RO",
       "Guest Access": "RO",
       "Migration TD Access": "RO",
       "Host VMM Rd Mask for a Production TD ": "-1",
       "Host VMM Wr Mask for a Production TD ": "0",
       "Host VMM Rd Mask for a Debug TD ": "-1",
       "Host VMM Wr Mask for a Debug TD ": "0",
       "Guest Rd Mask": "-1",
       "Guest Wr Mask": "0",
       "Migration TD Rd Mask": "-1",
       "Migration TD wr Mask": "0"
     },