On Fri, Feb 05, 2021 at 03:38:22PM -0800, Kuppuswamy Sathyanarayanan wrote:
> From: "Kirill A. Shutemov" <kirill.shute...@linux.intel.com>
>
> The TDX module injects #VE exception to the guest TD in cases of
> disallowed instructions, disallowed MSR accesses and subset of CPUID
> leaves. Also, it's theoretically possible for CPU to inject #VE
> exception on EPT violation, but the TDX module makes sure this does
> not happen, as long as all memory used is properly accepted using
> TDCALLs. You can find more details about it in, Guest-Host-Communication
> Interface (GHCI) for Intel Trust Domain Extensions (Intel TDX)
> specification, sec 2.3.
>
> Add basic infrastructure to handle #VE. If there is no handler for a
> given #VE, since its a unexpected event (fault case), treat it as a
> general protection fault and handle it using do_general_protection()
> call.
>
> TDCALL[TDGETVEINFO] provides information about #VE such as exit reason.
>
> More details on cases where #VE exceptions are allowed/not-allowed:
>
> The #VE exception do not occur in the paranoid entry paths, like NMIs.
> While other operations during an NMI might cause #VE, these are in the
> NMI code that can handle nesting, so there is no concern about
> reentrancy. This is similar to how #PF is handled in NMIs.
>
> The #VE exception also cannot happen in entry/exit code with the
> wrong gs, such as the SWAPGS code, so it's entry point does not
> need "paranoid" handling.
All of the above are arranged by using the below secure EPT for init
text and data?
> Any memory accesses can cause #VE if it causes an EPT
> violation. However, the VMM is only in direct control of some of the
> EPT tables. The Secure EPT tables are controlled by the TDX module
> which guarantees no EPT violations will result in #VE for the guest,
> once the memory has been accepted.
Which is supposedly then set up to avoid #VE during the syscall gap,
yes? Which then results in #VE not having to be IST.
> +#ifdef CONFIG_INTEL_TDX_GUEST
> +DEFINE_IDTENTRY(exc_virtualization_exception)
> +{
> + struct ve_info ve;
> + int ret;
> +
> + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
> +
> + /* Consume #VE info before re-enabling interrupts */
So what happens if NMI happens here, and triggers a nested #VE ?
> + ret = tdx_get_ve_info(&ve);
> + cond_local_irq_enable(regs);
> + if (!ret)
> + ret = tdx_handle_virtualization_exception(regs, &ve);
> + /*
> + * If #VE exception handler could not handle it successfully, treat
> + * it as #GP(0) and handle it.
> + */
> + if (ret)
> + do_general_protection(regs, 0);
> + cond_local_irq_disable(regs);
> +}
> +#endif
