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

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Date: Fri, 17 May 2024 19:25:00 +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 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
+
+#define TDCS_CONFIG_NO_RBP_MOD		BIT_ULL(2)
+
+/* Read TD-scoped metadata */
+static inline u64 tdg_vm_rd(u64 field, u64 *value)
+{
+	struct tdx_module_args args = {
+		.rdx = field,
+	};
+	u64 ret;
+
+	ret = __tdcall_ret(TDG_VM_RD, &args);
+	*value = args.r8;
+
+	return ret;
+}
+
 void __init tdx_early_init(void)
 {
 	struct tdx_module_args args = {
 		.rdx = TDCS_NOTIFY_ENABLES,
 		.r9 = -1ULL,
 	};
-	u64 cc_mask;
+	u64 cc_mask, config;
 	u32 eax, sig[3];
 
 	cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &sig[0], &sig[2],  &sig[1]);
@@ -893,4 +913,7 @@ void __init tdx_early_init(void)
 	x86_cpuinit.parallel_bringup = false;
 
 	pr_info("Guest detected\n");
+
+	tdg_vm_rd(TDCS_CONFIG_FLAGS, &config);
+	printk("NO_RBP_MOD: %#llx\n", config & TDCS_CONFIG_NO_RBP_MOD);
 }
-- 
  Kiryl Shutsemau / Kirill A. Shutemov