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

Kirill A. Shutemov
2024-05-17T16:25:05Z

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@intel.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