linux-kernel - [PATCH v3 1/1] x86/tdx: Handle MWAIT, MONITOR and WBINVD

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Date:   Mon, 29 Mar 2021 16:16:15 -0700
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: [PATCH v3 1/1] 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
appropriately.

Since the impact of executing WBINVD instruction in non ring-0 mode
can be heavy, use BUG() to report it. For others, raise a WARNING
message.

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

Changes since v2:
 * Added BUG() for WBINVD, WARN for MONITOR instructions.
 * Fixed comments as per Dave's review.

Changes since v1:
 * Added WARN() for MWAIT #VE exception.

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 | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
index e936b2f88bf6..4c6336a055a3 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 +365,32 @@ int tdg_handle_virtualization_exception(struct pt_regs *regs,
 	case EXIT_REASON_EPT_VIOLATION:
 		ve->instr_len = tdg_handle_mmio(regs, ve);
 		break;
+	case EXIT_REASON_WBINVD:
+		/*
+		 * WBINVD is a privileged instruction, can only be executed
+		 * in ring 0. Since we reached here, the kernel is in buggy
+		 * state.
+		 */
+		pr_err("WBINVD #VE Exception\n");
+		BUG();
+		break;
+	case EXIT_REASON_MONITOR_INSTRUCTION:
+		/*
+		 * MONITOR is a privileged instruction, can only be executed
+		 * in ring 0. So we are not supposed to reach here. Raise a
+		 * warning message.
+		 */
+		WARN(1, "MONITOR unexpected #VE Exception\n");
+		break;
+	case EXIT_REASON_MWAIT_INSTRUCTION:
+		/*
+		 * MWAIT feature is suppressed in firmware and in
+		 * tdx_early_init() by clearing X86_FEATURE_MWAIT CPU feature
+		 * flag. Since we are not supposed to reach here, raise a
+		 * warning message and return -EFAULT.
+		 */
+		WARN(1, "MWAIT unexpected #VE Exception\n");
+		return -EFAULT;
 	default:
 		pr_warn("Unexpected #VE: %d\n", ve->exit_reason);
 		return -EFAULT;
-- 
2.25.1