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

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On 23.05.24 12:35, Kirill A. Shutemov wrote:
On Fri, May 17, 2024 at 07:25:01PM +0300, 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@xxxxxxxxx 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?

Jürgen, have you tried it?


No, I'm not yet at the point where I can boot a guest successfully.


Juergen




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