Real mode interrupt injection emulation

From: Mohammed Gamal <[email protected]>

Replace the inject-as-software-interrupt hack we currently have with emulated injection.

Signed-off-by Mohammed Gamal <[email protected]>

Signed-off-by Avi Kivity <[email protected]>

---
 arch/x86/kvm/vmx.c |   65 ++++-----------------------------------------------
 1 files changed, 6 insertions(+), 59 deletions(-)

arch/x86/kvm/vmx.c +6 -56

index 8ef6199..2572153 100644
@@ -155,11 +155,6 @@ struct vcpu_vmx {
 			u32 limit;
 			u32 ar;
 		} tr, es, ds, fs, gs;
-		struct {
-			bool pending;
-			u8 vector;
-			unsigned rip;
-		} irq;
 	} rmode;
 	int vpid;
 	bool emulation_required;

@@ -1034,16 +1029,8 @@ static void vmx_queue_exception(struct kvm_vcpu *vcpu, unsigned nr,
 	}
 
 	if (vmx->rmode.vm86_active) {
-		vmx->rmode.irq.pending = true;
-		vmx->rmode.irq.vector = nr;
-		vmx->rmode.irq.rip = kvm_rip_read(vcpu);
-		if (kvm_exception_is_soft(nr))
-			vmx->rmode.irq.rip +=
-				vmx->vcpu.arch.event_exit_inst_len;
-		intr_info |= INTR_TYPE_SOFT_INTR;
-		vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, intr_info);
-		vmcs_write32(VM_ENTRY_INSTRUCTION_LEN, 1);
-		kvm_rip_write(vcpu, vmx->rmode.irq.rip - 1);
+		if (kvm_inject_realmode_interrupt(vcpu, nr) != EMULATE_DONE)
+			kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
 		return;
 	}
 

@@ -2822,16 +2809,8 @@ static void vmx_inject_irq(struct kvm_vcpu *vcpu)
 
 	++vcpu->stat.irq_injections;
 	if (vmx->rmode.vm86_active) {
-		vmx->rmode.irq.pending = true;
-		vmx->rmode.irq.vector = irq;
-		vmx->rmode.irq.rip = kvm_rip_read(vcpu);
-		if (vcpu->arch.interrupt.soft)
-			vmx->rmode.irq.rip +=
-				vmx->vcpu.arch.event_exit_inst_len;
-		vmcs_write32(VM_ENTRY_INTR_INFO_FIELD,
-			     irq | INTR_TYPE_SOFT_INTR | INTR_INFO_VALID_MASK);
-		vmcs_write32(VM_ENTRY_INSTRUCTION_LEN, 1);
-		kvm_rip_write(vcpu, vmx->rmode.irq.rip - 1);
+		if (kvm_inject_realmode_interrupt(vcpu, irq) != EMULATE_DONE)
+			kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
 		return;
 	}
 	intr = irq | INTR_INFO_VALID_MASK;

@@ -2863,14 +2842,8 @@ static void vmx_inject_nmi(struct kvm_vcpu *vcpu)
 
 	++vcpu->stat.nmi_injections;
 	if (vmx->rmode.vm86_active) {
-		vmx->rmode.irq.pending = true;
-		vmx->rmode.irq.vector = NMI_VECTOR;
-		vmx->rmode.irq.rip = kvm_rip_read(vcpu);
-		vmcs_write32(VM_ENTRY_INTR_INFO_FIELD,
-			     NMI_VECTOR | INTR_TYPE_SOFT_INTR |
-			     INTR_INFO_VALID_MASK);
-		vmcs_write32(VM_ENTRY_INSTRUCTION_LEN, 1);
-		kvm_rip_write(vcpu, vmx->rmode.irq.rip - 1);
+		if (kvm_inject_realmode_interrupt(vcpu, NMI_VECTOR) != EMULATE_DONE)
+			kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
 		return;
 	}
 	vmcs_write32(VM_ENTRY_INTR_INFO_FIELD,

@@ -3832,29 +3805,6 @@ static void vmx_recover_nmi_blocking(struct vcpu_vmx *vmx)
 			ktime_to_ns(ktime_sub(ktime_get(), vmx->entry_time));
 }
 
-/*
- * Failure to inject an interrupt should give us the information
- * in IDT_VECTORING_INFO_FIELD.  However, if the failure occurs
- * when fetching the interrupt redirection bitmap in the real-mode
- * tss, this doesn't happen.  So we do it ourselves.
- */
-static void fixup_rmode_irq(struct vcpu_vmx *vmx, u32 *idt_vectoring_info)
-{
-	vmx->rmode.irq.pending = 0;
-	if (kvm_rip_read(&vmx->vcpu) + 1 != vmx->rmode.irq.rip)
-		return;
-	kvm_rip_write(&vmx->vcpu, vmx->rmode.irq.rip);
-	if (*idt_vectoring_info & VECTORING_INFO_VALID_MASK) {
-		*idt_vectoring_info &= ~VECTORING_INFO_TYPE_MASK;
-		*idt_vectoring_info |= INTR_TYPE_EXT_INTR;
-		return;
-	}
-	*idt_vectoring_info =
-		VECTORING_INFO_VALID_MASK
-		| INTR_TYPE_EXT_INTR
-		| vmx->rmode.irq.vector;
-}
-
 static void __vmx_complete_interrupts(struct vcpu_vmx *vmx,
 				      u32 idt_vectoring_info,
 				      int instr_len_field,

arch/x86/kvm/vmx.c +0 -0

 	idtv_info_valid = idt_vectoring_info & VECTORING_INFO_VALID_MASK;
 
 	vmx->vcpu.arch.nmi_injected = false;

Signature · 1 line

1.7.2.3

Quoted 7 lines

static void __vmx_complete_interrupts(struct vcpu_vmx *vmx,
u32 idt_vectoring_info,
int instr_len_field,
@@ -3864,9 +3814,6 @@ static void __vmx_complete_interrupts(struct vcpu_vmx *vmx,
int type;
bool idtv_info_valid;

Quoted 3 lines

- if (vmx->rmode.irq.pending)
- fixup_rmode_irq(vmx,&idt_vectoring_info);
-

Don't you have to undo kvm_inject_realmode_interrupt if injection fails?

Quoted 7 lines · Marcelo Tosatti

Quoted 7 lines

static void __vmx_complete_interrupts(struct vcpu_vmx *vmx,
u32 idt_vectoring_info,
int instr_len_field,
@@ -3864,9 +3814,6 @@ static void __vmx_complete_interrupts(struct vcpu_vmx *vmx,
int type;
bool idtv_info_valid;

Quoted 7 lines

Quoted 3 lines

- if (vmx->rmode.irq.pending)
- fixup_rmode_irq(vmx,&idt_vectoring_info);
-

Don't you have to undo kvm_inject_realmode_interrupt if injection fails?

Injection cannot fail (at least, in the same sense as the vmx injections). It's actually not about failures, it's about guest entry being cancelled due to a signal or some KVM_REQ that needs attention. For vmx style injections, we need to undo the injection to keep things in a consistent state. To realmode emulated injection, everything is in a consistent state already, so no need to undo anything (it's also impossible, since we overwrote memory on the stack).

Quoted 16 lines · Avi Kivity

Quoted 7 lines · Marcelo Tosatti

Quoted 7 lines

static void __vmx_complete_interrupts(struct vcpu_vmx *vmx,
u32 idt_vectoring_info,
int instr_len_field,
@@ -3864,9 +3814,6 @@ static void __vmx_complete_interrupts(struct vcpu_vmx *vmx,

   	int type;
   	bool idtv_info_valid;

Quoted 7 lines

Quoted 3 lines

  -	if (vmx->rmode.irq.pending)
  -		fixup_rmode_irq(vmx,&idt_vectoring_info);
  -

Don't you have to undo kvm_inject_realmode_interrupt if injection fails?

Quoted 8 lines

Injection cannot fail (at least, in the same sense as the vmx injections). It's actually not about failures, it's about guest entry being cancelled due to a signal or some KVM_REQ that needs attention. For vmx style injections, we need to undo the injection to keep things in a consistent state. To realmode emulated injection, everything is in a consistent state already, so no need to undo anything (it's also impossible, since we overwrote memory on the stack).

Aren't you going to push EFLAGS,CS,EIP on the stack twice if that occurs?

Our current real mode interrupt injection injects external interrupts as software interrupts, which is somewhat hacky. This is problematic in big real mode (can't use vmx there) and on via processors (a cpu bug prevents this from working correctly).

Replace the current mechanism with emulation; we now inject the interrupt by looking up the vector in the IVT, updating the stack, etc. using the emulator. This is somewhat slower but works in all cases.

Our current real mode interrupt injection injects external interrupts as software interrupts, which is somewhat hacky. This is problematic in big real mode (can't use vmx there) and on via processors (a cpu bug prevents this from working correctly).

Replace the current mechanism with emulation; we now inject the interrupt by looking up the vector in the IVT, updating the stack, etc. using the emulator. This is somewhat slower but works in all cases.

Avi Kivity (1):
KVM: VMX: Respect interrupt window in big real mode

Mohammed Gamal (3):
KVM: x86 emulator: Expose emulate_int_real()
KVM: Add kvm_inject_realmode_interrupt() wrapper
KVM: VMX: Emulated real mode interrupt injection

 arch/x86/include/asm/kvm_emulate.h |    3 +-
 arch/x86/kvm/vmx.c                 |   74 +++++++----------------------------
 arch/x86/kvm/x86.c                 |   29 ++++++++++++++
 arch/x86/kvm/x86.h                 |    1 +
 4 files changed, 47 insertions(+), 60 deletions(-)

Signature · 1 line

1.7.2.3