KVM: TDX: Handle EPT violation/misconfig exit

KVM: TDX: Handle EPT violation/misconfig exit

For TDX, on EPT violation, call common __vmx_handle_ept_violation() to
trigger x86 MMU code; on EPT misconfiguration, bug the VM since it
shouldn't happen.

EPT violation due to instruction fetch should never be triggered from
shared memory in TDX guest.  If such EPT violation occurs, treat it as
broken hardware.

EPT misconfiguration shouldn't happen on neither shared nor secure EPT for
TDX guests.
- TDX module guarantees no EPT misconfiguration on secure EPT.  Per TDX
  module v1.5 spec section 9.4 "Secure EPT Induced TD Exits":
  "By design, since secure EPT is fully controlled by the TDX module, an
  EPT misconfiguration on a private GPA indicates a TDX module bug and is
  handled as a fatal error."
- For shared EPT, the MMIO caching optimization, which is the only case
  where current KVM configures EPT entries to generate EPT
  misconfiguration, is implemented in a different way for TDX guests.  KVM
  configures EPT entries to non-present value without suppressing #VE bit.
  It causes #VE in the TDX guest and the guest will call TDG.VP.VMCALL to
  request MMIO emulation.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Co-developed-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
[binbin: rework changelog]
Co-developed-by: Binbin Wu <binbin.wu@linux.intel.com>
Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
Message-ID: <20250227012021.1778144-2-binbin.wu@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>