[PATCH 6/7] KVM: VMX: Provide separate subroutines for invoking NMI vs. IRQ handlers

Sean Christopherson
2022-12-13T06:10:05Z

Split the asm subroutines for handling NMIs versus IRQs that occur in the
guest so that the NMI handler can be called from a noinstr section. As a
bonus, the NMI path doesn't need an indirect branch.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/vmx/vmenter.S | 70 +++++++++++++++++++++-----------------
arch/x86/kvm/vmx/vmx.c | 26 ++++++--------
2 files changed, 50 insertions(+), 46 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S
index 766c6b3ef5ed..9d987e7e48c4 100644
--- a/arch/x86/kvm/vmx/vmenter.S
+++ b/arch/x86/kvm/vmx/vmenter.S
@@ -31,6 +31,39 @@
#define VCPU_R15 __VCPU_REGS_R15 * WORD_SIZE
#endif

+.macro VMX_DO_EVENT_IRQOFF call_insn call_target
+ /*
+ * Unconditionally create a stack frame, getting the correct RSP on the
+ * stack (for x86-64) would take two instructions anyways, and RBP can
+ * be used to restore RSP to make objtool happy (see below).
+ */
+ push %_ASM_BP
+ mov %_ASM_SP, %_ASM_BP
+
+#ifdef CONFIG_X86_64
+ /*
+ * Align RSP to a 16-byte boundary (to emulate CPU behavior) before
+ * creating the synthetic interrupt stack frame for the IRQ/NMI.
+ */
+ and $-16, %rsp
+ push $__KERNEL_DS
+ push %rbp
+#endif
+ pushf
+ push $__KERNEL_CS
+ \call_insn \call_target
+
+ /*
+ * "Restore" RSP from RBP, even though IRET has already unwound RSP to
+ * the correct value. objtool doesn't know the callee will IRET and,
+ * without the explicit restore, thinks the stack is getting walloped.
+ * Using an unwind hint is problematic due to x86-64's dynamic alignment.
+ */
+ mov %_ASM_BP, %_ASM_SP
+ pop %_ASM_BP
+ RET
+.endm
+
.section .noinstr.text, "ax"

/**
@@ -320,35 +353,10 @@ SYM_FUNC_START(vmread_error_trampoline)
SYM_FUNC_END(vmread_error_trampoline)
#endif

-SYM_FUNC_START(vmx_do_interrupt_nmi_irqoff)
- /*
- * Unconditionally create a stack frame, getting the correct RSP on the
- * stack (for x86-64) would take two instructions anyways, and RBP can
- * be used to restore RSP to make objtool happy (see below).
- */
- push %_ASM_BP
- mov %_ASM_SP, %_ASM_BP
+SYM_FUNC_START(vmx_do_nmi_irqoff)
+ VMX_DO_EVENT_IRQOFF call asm_exc_nmi_kvm_vmx
+SYM_FUNC_END(vmx_do_nmi_irqoff)

-#ifdef CONFIG_X86_64
- /*
- * Align RSP to a 16-byte boundary (to emulate CPU behavior) before
- * creating the synthetic interrupt stack frame for the IRQ/NMI.
- */
- and $-16, %rsp
- push $__KERNEL_DS
- push %rbp
-#endif
- pushf
- push $__KERNEL_CS
- CALL_NOSPEC _ASM_ARG1
-
- /*
- * "Restore" RSP from RBP, even though IRET has already unwound RSP to
- * the correct value. objtool doesn't know the callee will IRET and,
- * without the explicit restore, thinks the stack is getting walloped.
- * Using an unwind hint is problematic due to x86-64's dynamic alignment.
- */
- mov %_ASM_BP, %_ASM_SP
- pop %_ASM_BP
- RET
-SYM_FUNC_END(vmx_do_interrupt_nmi_irqoff)
+SYM_FUNC_START(vmx_do_interrupt_irqoff)
+ VMX_DO_EVENT_IRQOFF CALL_NOSPEC _ASM_ARG1
+SYM_FUNC_END(vmx_do_interrupt_irqoff)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 7ace22ee240d..c242e2591896 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6786,17 +6786,8 @@ static void vmx_apicv_post_state_restore(struct kvm_vcpu *vcpu)
memset(vmx->pi_desc.pir, 0, sizeof(vmx->pi_desc.pir));
}

-void vmx_do_interrupt_nmi_irqoff(unsigned long entry);
-
-static void handle_interrupt_nmi_irqoff(struct kvm_vcpu *vcpu,
- unsigned long entry)
-{
- bool is_nmi = entry == (unsigned long)asm_exc_nmi_kvm_vmx;
-
- kvm_before_interrupt(vcpu, is_nmi ? KVM_HANDLING_NMI : KVM_HANDLING_IRQ);
- vmx_do_interrupt_nmi_irqoff(entry);
- kvm_after_interrupt(vcpu);
-}
+void vmx_do_interrupt_irqoff(unsigned long entry);
+void vmx_do_nmi_irqoff(void);

static void handle_nm_fault_irqoff(struct kvm_vcpu *vcpu)
{
@@ -6820,7 +6811,6 @@ static void handle_nm_fault_irqoff(struct kvm_vcpu *vcpu)

static void handle_exception_nmi_irqoff(struct vcpu_vmx *vmx)
{
- const unsigned long nmi_entry = (unsigned long)asm_exc_nmi_kvm_vmx;
u32 intr_info = vmx_get_intr_info(&vmx->vcpu);

/* if exit due to PF check for async PF */
@@ -6833,8 +6823,11 @@ static void handle_exception_nmi_irqoff(struct vcpu_vmx *vmx)
else if (is_machine_check(intr_info))
kvm_machine_check();
/* We need to handle NMIs before interrupts are enabled */
- else if (is_nmi(intr_info))
- handle_interrupt_nmi_irqoff(&vmx->vcpu, nmi_entry);
+ else if (is_nmi(intr_info)) {
+ kvm_before_interrupt(&vmx->vcpu, KVM_HANDLING_NMI);
+ vmx_do_nmi_irqoff();
+ kvm_after_interrupt(&vmx->vcpu);
+ }
}

static void handle_external_interrupt_irqoff(struct kvm_vcpu *vcpu)
@@ -6847,7 +6840,10 @@ static void handle_external_interrupt_irqoff(struct kvm_vcpu *vcpu)
"KVM: unexpected VM-Exit interrupt info: 0x%x", intr_info))
return;

- handle_interrupt_nmi_irqoff(vcpu, gate_offset(desc));
+ kvm_before_interrupt(vcpu, KVM_HANDLING_IRQ);
+ vmx_do_interrupt_irqoff(gate_offset(desc));
+ kvm_after_interrupt(vcpu);
+
vcpu->arch.at_instruction_boundary = true;
}

--
2.39.0.rc1.256.g54fd8350bd-goog