Re: [PATCH v3 1/2] x86/kvm/vmx: Move IRQ/NMI dispatch from KVM into x86 core

[Peter Zijlstra]

Sorry, I missed this :/

On Wed, May 20, 2026 at 04:06:21PM -0700, Nathan Chancellor wrote:
> On Fri, May 08, 2026 at 11:18:29AM +0200, Peter Zijlstra wrote:
> > 
> > Move the VMX interrupt dispatch magic into the x86 core code. This
> > isolates KVM from the FRED/IDT decisions and reduces the amount of
> > EXPORT_SYMBOL_FOR_KVM().
> > 
> > Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> > Tested-by: "Verma, Vishal L" <vishal.l.verma@xxxxxxxxx>
> 
> I am seeing
> 
>   vmlinux.o: warning: objtool: idt_do_interrupt_irqoff+0xe: no-cfi indirect call!
> 
> after this landed in -next.
> 
>   $ cat arch/x86/configs/repro.config
>   CONFIG_CFI=y
>   CONFIG_KVM=y
>   CONFIG_KVM_INTEL=y
> 
>   $ make -skj"$(nproc)" ARCH=x86_64 LLVM=1 mrproper defconfig repro.config vmlinux
>   vmlinux.o: warning: objtool: idt_do_interrupt_irqoff+0xe: no-cfi indirect call!
> 

Durr.

---
Subject: x86/kvm/vmx: Fix x86_64 CFI build

I missed that idt_do_interrupt_irqoff() gets compiled on x84_64; this is
a problem for CFI builds because it includes an unadorned indirect call.
It is however completely dead code.

Rework things to not emit this function at all.

Fixes: 0701c9e17bd9 ("x86/kvm/vmx: Move IRQ/NMI dispatch from KVM into x86 core")
Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Reported-by: Calvin Owens <calvin@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 06c7c6ebd6f9..14cd43d4da6c 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -55,7 +55,7 @@ noinstr void x86_entry_from_kvm(unsigned int event_type, unsigned int vector)
 	 * The FRED NMI context is significantly different and will not work
 	 * right (specifically FRED fixed the NMI recursion issue).
 	 */
-	idt_entry_from_kvm(vector);
+	idt_do_nmi_irqoff();
 }
 EXPORT_SYMBOL_FOR_KVM(x86_entry_from_kvm);
 #endif
diff --git a/arch/x86/entry/entry.S b/arch/x86/entry/entry.S
index a56e043b266d..2bc217bb5475 100644
--- a/arch/x86/entry/entry.S
+++ b/arch/x86/entry/entry.S
@@ -109,11 +109,13 @@ EXPORT_SYMBOL(__ref_stack_chk_guard);
 	RET
 .endm
 
+#ifndef CONFIG_X86_64
 .pushsection .text, "ax"
 SYM_FUNC_START(idt_do_interrupt_irqoff)
 	IDT_DO_EVENT_IRQOFF CALL_NOSPEC _ASM_ARG1
 SYM_FUNC_END(idt_do_interrupt_irqoff)
 .popsection
+#endif
 
 .pushsection .noinstr.text, "ax"
 SYM_FUNC_START(idt_do_nmi_irqoff)
diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c
index 7bcf1decc034..90a22e24a9eb 100644
--- a/arch/x86/kernel/idt.c
+++ b/arch/x86/kernel/idt.c
@@ -268,18 +268,10 @@ void __init idt_setup_early_pf(void)
 }
 #endif
 
-#if IS_ENABLED(CONFIG_KVM_INTEL)
-noinstr void idt_entry_from_kvm(unsigned int vector)
+#if IS_ENABLED(CONFIG_KVM_INTEL) && !defined(CONFIG_X86_64)
+void idt_entry_from_kvm(unsigned int vector)
 {
-	if (vector == NMI_VECTOR)
-		return idt_do_nmi_irqoff();
-
-	/*
-	 * Only the NMI path requires noinstr.
-	 */
-	instrumentation_begin();
 	idt_do_interrupt_irqoff(gate_offset(idt_table + vector));
-	instrumentation_end();
 }
 #endif