FAILED: patch "[PATCH] KVM: nSVM: Always intercept VMMCALL when L2 is active" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 33d3617a52f9930d22b2af59f813c2fbdefa6dd5
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026050319-frequency-badge-f9fe@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 33d3617a52f9930d22b2af59f813c2fbdefa6dd5 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <[email protected]>
Date: Tue, 3 Mar 2026 16:22:23 -0800
Subject: [PATCH] KVM: nSVM: Always intercept VMMCALL when L2 is active

Always intercept VMMCALL now that KVM properly synthesizes a #UD as appropriate, i.e. when L1 doesn't want to intercept VMMCALL, to avoid putting L2 into an infinite #UD loop if KVM_X86_QUIRK_FIX_HYPERCALL_INSN is enabled.

By letting L2 execute VMMCALL natively and thus #UD, for all intents and purposes KVM morphs the VMMCALL intercept into a #UD intercept (KVM always intercepts #UD). When the hypercall quirk is enabled, KVM "emulates" VMMCALL in response to the #UD by trying to fixup the opcode to the "right" vendor, then restarts the guest, without skipping the VMMCALL. As a result, the guest sees an endless stream of #UDs since it's already executing the correct vendor hypercall instruction, i.e. the emulator doesn't anticipate that the #UD could be due to lack of interception, as opposed to a truly undefined opcode.

index 9af03970d40c..f70d076911a6 100644
@@ -51,10 +51,6 @@ static inline bool nested_svm_is_l2_tlb_flush_hcall(struct kvm_vcpu *vcpu)
 void svm_hv_inject_synthetic_vmexit_post_tlb_flush(struct kvm_vcpu *vcpu);
 #else /* CONFIG_KVM_HYPERV */
 static inline void nested_svm_hv_update_vm_vp_ids(struct kvm_vcpu *vcpu) {}
-static inline bool nested_svm_l2_tlb_flush_enabled(struct kvm_vcpu *vcpu)
-{
-	return false;
-}
 static inline bool nested_svm_is_l2_tlb_flush_hcall(struct kvm_vcpu *vcpu)
 {
 	return false;

index 0f7893a7cb04..fb86f09985e7 100644
@@ -158,13 +158,6 @@ void recalc_intercepts(struct vcpu_svm *svm)
 			vmcb_clr_intercept(c, INTERCEPT_VINTR);
 	}
 
-	/*
-	 * We want to see VMMCALLs from a nested guest only when Hyper-V L2 TLB
-	 * flush feature is enabled.
-	 */
-	if (!nested_svm_l2_tlb_flush_enabled(&svm->vcpu))
-		vmcb_clr_intercept(c, INTERCEPT_VMMCALL);
-
 	for (i = 0; i < MAX_INTERCEPT; i++)
 		c->intercepts[i] |= g->intercepts[i];