linux-kernel - [PATCH 1/2] KVM: SVM: Drop the module param to control SEV-ES DebugSwap

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Message-ID: <20260109033101.1005769-2-seanjc@google.com>
Date: Thu,  8 Jan 2026 19:31:00 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Tom Lendacky <thomas.lendacky@....com>
Subject: [PATCH 1/2] KVM: SVM: Drop the module param to control SEV-ES DebugSwap

Rip out the DebugSwap module param, as the sequence of events that led to
its inclusion was one big mistake, the param no longer serves any purpose.

Commit d1f85fbe836e ("KVM: SEV: Enable data breakpoints in SEV-ES") goofed
by not adding a way for the userspace VMM to control the feature.
Functionally, that was fine, but it broke attestation signatures because
SEV_FEATURES are included in the signature.

Commit 5abf6dceb066 ("SEV: disable SEV-ES DebugSwap by default") fixed that
issue, but the underlying flaw of userspace not having a way to control
SEV_FEATURES was still there.

That flaw was addressed by commit 4f5defae7089 ("KVM: SEV: introduce
KVM_SEV_INIT2 operation"), and so then 4dd5ecacb9a4 ("KVM: SEV: allow
SEV-ES DebugSwap again") re-enabled DebugSwap by default.

Now that the dust has settled, the module param doesn't serve any
meaningful purpose.

Cc: Tom Lendacky <thomas.lendacky@....com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/sev.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index f59c65abe3cf..9b92f0cccfe6 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -53,9 +53,6 @@ module_param_named(sev_es, sev_es_enabled, bool, 0444);
 static bool sev_snp_enabled = true;
 module_param_named(sev_snp, sev_snp_enabled, bool, 0444);

-/* enable/disable SEV-ES DebugSwap support */
-static bool sev_es_debug_swap_enabled = true;
-module_param_named(debug_swap, sev_es_debug_swap_enabled, bool, 0444);
 static u64 sev_supported_vmsa_features;

 static unsigned int nr_ciphertext_hiding_asids;
@@ -3150,12 +3147,10 @@ void __init sev_hardware_setup(void)
 	sev_es_enabled = sev_es_supported;
 	sev_snp_enabled = sev_snp_supported;

-	if (!sev_es_enabled || !cpu_feature_enabled(X86_FEATURE_DEBUG_SWAP) ||
-	    !cpu_feature_enabled(X86_FEATURE_NO_NESTED_DATA_BP))
-		sev_es_debug_swap_enabled = false;
-
 	sev_supported_vmsa_features = 0;
-	if (sev_es_debug_swap_enabled)
+
+	if (sev_es_enabled && cpu_feature_enabled(X86_FEATURE_DEBUG_SWAP) &&
+	    cpu_feature_enabled(X86_FEATURE_NO_NESTED_DATA_BP))
 		sev_supported_vmsa_features |= SVM_SEV_FEAT_DEBUG_SWAP;

 	if (sev_snp_enabled && tsc_khz && cpu_feature_enabled(X86_FEATURE_SNP_SECURE_TSC))
-- 
2.52.0.457.g6b5491de43-goog