Minor (if there is such a thing for this code) cleanup of KVM's handling
of IRQ and NMI exits to move the invocation of the IRQ handler to a
standalone assembly routine, and to then consolidate the NMI handling to
use the same indirect call approach instead of using INTn.
The IRQ cleanup was suggested by Josh Poimboeuf in the context of a false
postive objtool warning[*]. I believe Josh intended to use UNWIND hints
instead of trickery to avoid objtool complaints. I opted for trickery in
the form of a redundant, but explicit, restoration of RSP after the hidden
IRET. AFAICT, there are no existing UNWIND hints that would let objtool
know that the stack is magically being restored, and adding a new hint to
save a single MOV <reg>, <reg> instruction seemed like overkill.
The NMI consolidation was loosely suggested by Andi Kleen. Andi's actual
suggestion was to export and directly call the NMI handler, but that's a
more involved change (unless I'm misunderstanding the wants of the NMI
handler), whereas piggybacking the IRQ code is simple and seems like a
worthwhile intermediate step.
[*] https://lkml.kernel.org/r/20200908205947.arryy75c5cvldps7@treble
Sean Christopherson (2):
KVM: VMX: Move IRQ invocation to assembly subroutine
KVM: VMX: Invoke NMI handler via indirect call instead of INTn
arch/x86/kvm/vmx/vmenter.S | 28 +++++++++++++++++
arch/x86/kvm/vmx/vmx.c | 61 +++++++++++---------------------------
2 files changed, 45 insertions(+), 44 deletions(-)
--
2.28.0
Rework NMI VM-Exit handling to invoke the kernel handler by function
call instead of INTn. INTn microcode is relatively expensive, and
aligning the IRQ and NMI handling will make it easier to update KVM
should some newfangled method for invoking the handlers come along.
Suggested-by: Andi Kleen <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---
arch/x86/kvm/vmx/vmx.c | 30 +++++++++++++++---------------
1 file changed, 15 insertions(+), 15 deletions(-)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 391f079d9136..b0eca151931d 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6411,40 +6411,40 @@ static void vmx_apicv_post_state_restore(struct kvm_vcpu *vcpu)
void vmx_do_interrupt_nmi_irqoff(unsigned long entry);
+static void handle_interrupt_nmi_irqoff(struct kvm_vcpu *vcpu, u32 intr_info)
+{
+ unsigned int vector = intr_info & INTR_INFO_VECTOR_MASK;
+ gate_desc *desc = (gate_desc *)host_idt_base + vector;
+
+ kvm_before_interrupt(vcpu);
+ vmx_do_interrupt_nmi_irqoff(gate_offset(desc));
+ kvm_after_interrupt(vcpu);
+}
+
static void handle_exception_nmi_irqoff(struct vcpu_vmx *vmx)
{
u32 intr_info = vmx_get_intr_info(&vmx->vcpu);
/* if exit due to PF check for async PF */
- if (is_page_fault(intr_info)) {
+ if (is_page_fault(intr_info))
vmx->vcpu.arch.apf.host_apf_flags = kvm_read_and_reset_apf_flags();
/* Handle machine checks before interrupts are enabled */
- } else if (is_machine_check(intr_info)) {
+ 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)) {
- kvm_before_interrupt(&vmx->vcpu);
- asm("int $2");
- kvm_after_interrupt(&vmx->vcpu);
- }
+ else if (is_nmi(intr_info))
+ handle_interrupt_nmi_irqoff(&vmx->vcpu, intr_info);
}
static void handle_external_interrupt_irqoff(struct kvm_vcpu *vcpu)
{
- unsigned int vector;
- gate_desc *desc;
u32 intr_info = vmx_get_intr_info(vcpu);
if (WARN_ONCE(!is_external_intr(intr_info),
"KVM: unexpected VM-Exit interrupt info: 0x%x", intr_info))
return;
- vector = intr_info & INTR_INFO_VECTOR_MASK;
- desc = (gate_desc *)host_idt_base + vector;
-
- kvm_before_interrupt(vcpu);
- vmx_do_interrupt_nmi_irqoff(gate_offset(desc));
- kvm_after_interrupt(vcpu);
+ handle_interrupt_nmi_irqoff(vcpu, intr_info);
}
static void vmx_handle_exit_irqoff(struct kvm_vcpu *vcpu)
--
2.28.0