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Subject[PATCH v1 1/1] x86/tdx: Handle MWAIT, MONITOR and WBINVD
Date
In non-root TDX guest mode, MWAIT, MONITOR and WBINVD instructions
are not supported. So handle #VE due to these instructions as no ops.

Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
---

Changes since previous series:
* Suppressed MWAIT feature as per Andi's comment.
* Added warning debug log for MWAIT #VE exception.

arch/x86/kernel/tdx.c | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)

diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
index e936b2f88bf6..fb7d22b846fc 100644
--- a/arch/x86/kernel/tdx.c
+++ b/arch/x86/kernel/tdx.c
@@ -308,6 +308,9 @@ void __init tdx_early_init(void)

setup_force_cpu_cap(X86_FEATURE_TDX_GUEST);

+ /* MWAIT is not supported in TDX platform, so suppress it */
+ setup_clear_cpu_cap(X86_FEATURE_MWAIT);
+
tdg_get_info();

pv_ops.irq.safe_halt = tdg_safe_halt;
@@ -362,6 +365,26 @@ int tdg_handle_virtualization_exception(struct pt_regs *regs,
case EXIT_REASON_EPT_VIOLATION:
ve->instr_len = tdg_handle_mmio(regs, ve);
break;
+ /*
+ * Per Guest-Host-Communication Interface (GHCI) for Intel Trust
+ * Domain Extensions (Intel TDX) specification, sec 2.4,
+ * some instructions that unconditionally cause #VE (such as WBINVD,
+ * MONITOR, MWAIT) do not have corresponding TDCALL
+ * [TDG.VP.VMCALL <Instruction>] leaves, since the TD has been designed
+ * with no deterministic way to confirm the result of those operations
+ * performed by the host VMM. In those cases, the goal is for the TD
+ * #VE handler to increment the RIP appropriately based on the VE
+ * information provided via TDCALL.
+ */
+ case EXIT_REASON_WBINVD:
+ pr_warn_once("WBINVD #VE Exception\n");
+ case EXIT_REASON_MONITOR_INSTRUCTION:
+ /* Handle as nops. */
+ break;
+ case EXIT_REASON_MWAIT_INSTRUCTION:
+ /* MWAIT is supressed, not supposed to reach here. */
+ pr_warn("MWAIT unexpected #VE Exception\n");
+ return -EFAULT;
default:
pr_warn("Unexpected #VE: %d\n", ve->exit_reason);
return -EFAULT;
--
2.25.1
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