linux-kernel - [RFC v1 13/26] x86/tdx: Handle MWAIT, MONITOR and WBINVD

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Date:   Fri,  5 Feb 2021 15:38:30 -0800
From:   Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: [RFC v1 13/26] x86/tdx: Handle MWAIT, MONITOR and WBINVD

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@...ux.intel.com>
Reviewed-by: Andi Kleen <ak@...ux.intel.com>
---
 arch/x86/kernel/tdx.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
index eff58329751e..8d1d7555fb56 100644
--- a/arch/x86/kernel/tdx.c
+++ b/arch/x86/kernel/tdx.c
@@ -451,6 +451,23 @@ int tdx_handle_virtualization_exception(struct pt_regs *regs,
 	case EXIT_REASON_EPT_VIOLATION:
 		ve->instr_len = tdx_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_MWAIT_INSTRUCTION:
+	case EXIT_REASON_MONITOR_INSTRUCTION:
+		/* Handle as nops. */
+		break;
 	default:
 		pr_warn("Unexpected #VE: %d\n", ve->exit_reason);
 		return -EFAULT;
-- 
2.25.1