Re: [PATCH 2/7] KVM: TDX: Add a place holder for handler of TDX hypercalls (TDG.VP.VMCALL)

[Chao Gao <chao.gao@intel.com>]

On Sun, Dec 01, 2024 at 11:53:51AM +0800, Binbin Wu wrote:
>From: Isaku Yamahata <isaku.yamahata@intel.com>
>
>Add a place holder and related helper functions for preparation of
>TDG.VP.VMCALL handling.
>
>The TDX module specification defines TDG.VP.VMCALL API (TDVMCALL for short)
>for the guest TD to call hypercall to VMM.  When the guest TD issues a
>TDVMCALL, the guest TD exits to VMM with a new exit reason.  The arguments
>from the guest TD and returned values from the VMM are passed in the guest
>registers.  The guest RCX register indicates which registers are used.
>Define helper functions to access those registers.
>
>A new VMX exit reason TDCALL is added to indicate the exit is due to TDVMCALL
>from the guest TD.  Define the TDCALL exit reason and add a place holder to
>handle such exit.
>
>Co-developed-by: Xiaoyao Li <xiaoyao.li@intel.com>
>Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
>Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
>Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
>Co-developed-by: Binbin Wu <binbin.wu@linux.intel.com>
>Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>

Reviewed-by: Chao Gao <chao.gao@intel.com>

>---
>Hypercalls exit to userspace breakout:
>- Update changelog.
>- Drop the unused tdx->tdvmcall. (Chao)
>- Use TDVMCALL_STATUS prefix for TDX call status codes (Binbin)
>---
> arch/x86/include/uapi/asm/vmx.h |  4 ++-
> arch/x86/kvm/vmx/tdx.c          | 48 +++++++++++++++++++++++++++++++++
> 2 files changed, 51 insertions(+), 1 deletion(-)
>
>diff --git a/arch/x86/include/uapi/asm/vmx.h b/arch/x86/include/uapi/asm/vmx.h
>index a5faf6d88f1b..6a9f268a2d2c 100644
>--- a/arch/x86/include/uapi/asm/vmx.h
>+++ b/arch/x86/include/uapi/asm/vmx.h
>@@ -92,6 +92,7 @@
> #define EXIT_REASON_TPAUSE              68
> #define EXIT_REASON_BUS_LOCK            74
> #define EXIT_REASON_NOTIFY              75
>+#define EXIT_REASON_TDCALL              77
> 
> #define VMX_EXIT_REASONS \
> 	{ EXIT_REASON_EXCEPTION_NMI,         "EXCEPTION_NMI" }, \
>@@ -155,7 +156,8 @@
> 	{ EXIT_REASON_UMWAIT,                "UMWAIT" }, \
> 	{ EXIT_REASON_TPAUSE,                "TPAUSE" }, \
> 	{ EXIT_REASON_BUS_LOCK,              "BUS_LOCK" }, \
>-	{ EXIT_REASON_NOTIFY,                "NOTIFY" }
>+	{ EXIT_REASON_NOTIFY,                "NOTIFY" }, \
>+	{ EXIT_REASON_TDCALL,                "TDCALL" }

Side topic:
Strictly speaking, TDCALL vm-exit handling can happen for normal VMs. so, KVM may
need to handle it by injecting #UD. Of course, it is not necessary for this series.