On Thu, Jun 08, 2023 at 01:43:27AM +0000,
"Wang, Wei W" <wei.w.wang@xxxxxxxxx> wrote:
> On Thursday, June 8, 2023 2:16 AM, Isaku Yamahata wrote:
> > On Mon, Jun 05, 2023 at 03:20:19PM +0000, "Wang, Wei W"
> > <wei.w.wang@xxxxxxxxx> wrote:
> > > > +static inline u64 kvm_seamcall(u64 op, u64 rcx, u64 rdx, u64 r8, u64 r9,
> > > > + struct tdx_module_output *out) {
> > > > + u64 ret;
> > > > +
> > > > + ret = __seamcall(op, rcx, rdx, r8, r9, out);
> > > > + if (unlikely(ret == TDX_SEAMCALL_UD)) {
> > > > + /*
> > > > + * TDX requires VMXON or #UD. In the case of reboot or
> > > > kexec,
> > > > + * VMX is made off (VMXOFF) by kvm reboot notifier,
> > > > + * kvm_reboot(), while TDs are still running. The callers
> > > > check
> > > > + * the returned error and complain. Suppress it by returning 0.
> > > > + */
> > >
> > > Curious how do the callers check the returned error when " Suppress it
> > > by returning 0" here.
> >
> > It doesn't make sense for the caller to check the error and warn when
> > kvm_rebooting = true.
> > Let's make it "return kvm_rebooting ? 0 : ret;" instread of "return 0;".
> > Does it make sense?
>
> Seems no need. The comments look confusing, and not aligned to what
> the code achieves. From what I read:
> - if kvm_rebooting=true there: return 0 to caller and no error or warning happens
> - if kvm_rebooting=false there: crash the system via kvm_spurious_fault.
> In this non-rebooting case, I think the callers don’t get a chance to read the
> returned value and complain.
How about this comment?
if (unlikely(ret == TDX_SEAMCALL_UD)) {
/*
* TDX requires VMXON or #UD. In the case of reboot or kexec,
* kvm shutdown notifier, kvm_shutdown(), makes VMX off (VMXOFF)
* while TDs can be still running to invoke SEAMCALL. It
* results in superfluous errors or warnings.
* If rebooting, return 0 to suppress superfluous messages.
* If not rebooting, panic by kvm_spurious_fault().
*/
kvm_spurious_fault();
return 0;
}
> Another thing is, have you double-checked that invocation of seamcalls
> indeed returns TDX_SEAMCALL_UD when VMX=off?
I observed it several times during testing tdx module initialization. Here is
the example I dug out from my debug logs.
tdx: SEAMCALL failed: CPU 162 is not in VMX operation.
tdx: TDX module initialization failed (-22)
kvm_intel: Failed to initialize TDX module.
--
Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
