linux-kernel - [PATCH v4 4/7] x86/its: Use switch/case to apply mitigation

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Message-ID: <20250611-eibrs-fix-v4-4-5ff86cac6c61@linux.intel.com>
Date: Wed, 11 Jun 2025 10:29:47 -0700
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: x86@...nel.org
Cc: David Kaplan <david.kaplan@....com>, linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Nikolay Borisov <nik.borisov@...e.com>
Subject: [PATCH v4 4/7] x86/its: Use switch/case to apply mitigation

Prepare to apply stuffing mitigation in its_apply_mitigation(). This is
currently only done via retbleed mitigation. Also using switch/case makes
it evident that mitigation mode like VMEXIT_ONLY doesn't need any special
handling.

Reviewed-by: Nikolay Borisov <nik.borisov@...e.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
---
 arch/x86/kernel/cpu/bugs.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 20696abd1bef90aaf852fef1299b93d27c1f4da6..e861e8884d6b5e16f08d5bda0f47d5056d26c1f4 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1468,15 +1468,21 @@ static void __init its_update_mitigation(void)
 
 static void __init its_apply_mitigation(void)
 {
+	switch (its_mitigation) {
+	case ITS_MITIGATION_OFF:
+	case ITS_MITIGATION_AUTO:
+	case ITS_MITIGATION_VMEXIT_ONLY:
 	/* its=stuff forces retbleed stuffing and is enabled there. */
-	if (its_mitigation != ITS_MITIGATION_ALIGNED_THUNKS)
-		return;
-
-	if (!boot_cpu_has(X86_FEATURE_RETPOLINE))
-		setup_force_cpu_cap(X86_FEATURE_INDIRECT_THUNK_ITS);
+	case ITS_MITIGATION_RETPOLINE_STUFF:
+		break;
+	case ITS_MITIGATION_ALIGNED_THUNKS:
+		if (!boot_cpu_has(X86_FEATURE_RETPOLINE))
+			setup_force_cpu_cap(X86_FEATURE_INDIRECT_THUNK_ITS);
 
-	setup_force_cpu_cap(X86_FEATURE_RETHUNK);
-	set_return_thunk(its_return_thunk);
+		setup_force_cpu_cap(X86_FEATURE_RETHUNK);
+		set_return_thunk(its_return_thunk);
+		break;
+	}
 }
 
 #undef pr_fmt

-- 
2.34.1