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

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Date: Thu, 23 May 2024 13:35:17 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Jürgen Groß <jgross@...e.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 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@...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?

Jürgen, have you tried it?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov