Re: [PATCH v6 1/9] x86/fred, KVM: VMX: Pass event data to the FRED entry point from KVM

[Sean Christopherson <seanjc@google.com>]

On Tue, May 13, 2025, Sohil Mehta wrote:
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 5c5766467a61..1d43d4a2f6b6 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7079,7 +7079,7 @@ static void handle_external_interrupt_irqoff(struct kvm_vcpu *vcpu,
>  
>  	kvm_before_interrupt(vcpu, KVM_HANDLING_IRQ);
>  	if (cpu_feature_enabled(X86_FEATURE_FRED))
> -		fred_entry_from_kvm(EVENT_TYPE_EXTINT, vector);
> +		fred_entry_from_kvm(EVENT_TYPE_EXTINT, vector, 0);
>  	else
>  		vmx_do_interrupt_irqoff(gate_offset((gate_desc *)host_idt_base + vector));
>  	kvm_after_interrupt(vcpu);
> @@ -7393,7 +7393,8 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
>  	    is_nmi(vmx_get_intr_info(vcpu))) {
>  		kvm_before_interrupt(vcpu, KVM_HANDLING_NMI);
>  		if (cpu_feature_enabled(X86_FEATURE_FRED))
> -			fred_entry_from_kvm(EVENT_TYPE_NMI, NMI_VECTOR);
> +			fred_entry_from_kvm(EVENT_TYPE_NMI, NMI_VECTOR,
> +					    vmx_get_exit_qual(vcpu));
>  		else
>  			vmx_do_nmi_irqoff();
>  		kvm_after_interrupt(vcpu);

As a prep patch, what if we provide separate wrappers for IRQ vs. NMI?  That way
KVM doesn't need to shove a '0' literal for the IRQ case.  There isn't that much
code that's actually shared between the two, once you account for KVM having to
hardcode the NMI information.

Compile tested only...

--
From: Sean Christopherson <seanjc@google.com>
Date: Wed, 14 May 2025 07:07:55 -0700
Subject: [PATCH] x86/fred: Provide separate IRQ vs. NMI wrappers for "entry"
 from KVM

Provide separate wrappers for forwarding IRQs vs NMIs from KVM in
anticipation of adding support for NMI source reporting, which will add
an NMI-only parameter, i.e. will further pollute the current API with a
param that is a hardcoded for one of the two call sites.

Opportunistically tag the non-FRED NMI wrapper __always_inline, as the
compiler could theoretically generate a function call and trigger and a
(completely benign) "leaving noinstr" warning.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/include/asm/fred.h | 24 +++++++++++++++++++-----
 arch/x86/kvm/vmx/vmx.c      |  4 ++--
 2 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/fred.h b/arch/x86/include/asm/fred.h
index 2a29e5216881..dfb4f5e6a37a 100644
--- a/arch/x86/include/asm/fred.h
+++ b/arch/x86/include/asm/fred.h
@@ -10,6 +10,7 @@
 
 #include <asm/asm.h>
 #include <asm/trapnr.h>
+#include <asm/irq_vectors.h>
 
 /*
  * FRED event return instruction opcodes for ERET{S,U}; supported in
@@ -70,14 +71,26 @@ __visible void fred_entry_from_user(struct pt_regs *regs);
 __visible void fred_entry_from_kernel(struct pt_regs *regs);
 __visible void __fred_entry_from_kvm(struct pt_regs *regs);
 
-/* Can be called from noinstr code, thus __always_inline */
-static __always_inline void fred_entry_from_kvm(unsigned int type, unsigned int vector)
+/* Must be called from noinstr code, thus __always_inline */
+static __always_inline void fred_nmi_from_kvm(void)
 {
 	struct fred_ss ss = {
 		.ss     =__KERNEL_DS,
-		.type   = type,
+		.type   = EVENT_TYPE_NMI,
+		.vector = NMI_VECTOR,
+		.nmi    = true,
+		.lm     = 1,
+	};
+
+	asm_fred_entry_from_kvm(ss);
+}
+
+static inline void fred_irq_from_kvm(unsigned int vector)
+{
+	struct fred_ss ss = {
+		.ss     =__KERNEL_DS,
+		.type   = EVENT_TYPE_EXTINT,
 		.vector = vector,
-		.nmi    = type == EVENT_TYPE_NMI,
 		.lm     = 1,
 	};
 
@@ -109,7 +122,8 @@ static __always_inline unsigned long fred_event_data(struct pt_regs *regs) { ret
 static inline void cpu_init_fred_exceptions(void) { }
 static inline void cpu_init_fred_rsps(void) { }
 static inline void fred_complete_exception_setup(void) { }
-static inline void fred_entry_from_kvm(unsigned int type, unsigned int vector) { }
+static __always_inline void fred_nmi_from_kvm(void) { }
+static inline void fred_irq_from_kvm(unsigned int vector) { }
 static inline void fred_sync_rsp0(unsigned long rsp0) { }
 static inline void fred_update_rsp0(void) { }
 #endif /* CONFIG_X86_FRED */
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 5c5766467a61..271f92fee76b 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7079,7 +7079,7 @@ static void handle_external_interrupt_irqoff(struct kvm_vcpu *vcpu,
 
 	kvm_before_interrupt(vcpu, KVM_HANDLING_IRQ);
 	if (cpu_feature_enabled(X86_FEATURE_FRED))
-		fred_entry_from_kvm(EVENT_TYPE_EXTINT, vector);
+		fred_irq_from_kvm(vector);
 	else
 		vmx_do_interrupt_irqoff(gate_offset((gate_desc *)host_idt_base + vector));
 	kvm_after_interrupt(vcpu);
@@ -7393,7 +7393,7 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
 	    is_nmi(vmx_get_intr_info(vcpu))) {
 		kvm_before_interrupt(vcpu, KVM_HANDLING_NMI);
 		if (cpu_feature_enabled(X86_FEATURE_FRED))
-			fred_entry_from_kvm(EVENT_TYPE_NMI, NMI_VECTOR);
+			fred_nmi_from_kvm();
 		else
 			vmx_do_nmi_irqoff();
 		kvm_after_interrupt(vcpu);

base-commit: 9f35e33144ae5377d6a8de86dd3bd4d995c6ac65
--