Commit d618fb4e authored by Sean Christopherson's avatar Sean Christopherson
Browse files

KVM: x86: Fold WRMSR fastpath helpers into the main handler 

Fold the per-MSR WRMSR fastpath helpers into the main handler now that the
IPI path in particular is relatively tiny.  In addition to eliminating a
decent amount of boilerplate, this removes the ugly -errno/1/0 => bool
conversion (which is "necessitated" by kvm_x2apic_icr_write_fast()).

Opportunistically drop the comment about IPIs, as the purpose of the
fastpath is hopefully self-evident, and _if_ it needs more documentation,
the documentation (and rules!) should be placed in a more central location.

No functional change intended.

Link: https://lore.kernel.org/r/20250805190526.1453366-9-seanjc@google.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent aa2e4f02

arch/x86/kvm/x86.c

+5 −29
Original line number Diff line number Diff line
@@ -2134,48 +2134,24 @@ static inline bool kvm_vcpu_exit_request(struct kvm_vcpu *vcpu) 
	       kvm_request_pending(vcpu) || xfer_to_guest_mode_work_pending();

}



/*

 * The fast path for frequent and performance sensitive wrmsr emulation,

 * i.e. the sending of IPI, sending IPI early in the VM-Exit flow reduces

 * the latency of virtual IPI by avoiding the expensive bits of transitioning

 * from guest to host, e.g. reacquiring KVM's SRCU lock. In contrast to the

 * other cases which must be called after interrupts are enabled on the host.

 */

static int handle_fastpath_set_x2apic_icr_irqoff(struct kvm_vcpu *vcpu, u64 data)

{

	if (!lapic_in_kernel(vcpu) || !apic_x2apic_mode(vcpu->arch.apic))

		return 1;



	return kvm_x2apic_icr_write_fast(vcpu->arch.apic, data);

}



static int handle_fastpath_set_tscdeadline(struct kvm_vcpu *vcpu, u64 data)

{

	kvm_set_lapic_tscdeadline_msr(vcpu, data);

	return 0;

}



fastpath_t handle_fastpath_set_msr_irqoff(struct kvm_vcpu *vcpu)

{

	u64 data = kvm_read_edx_eax(vcpu);

	u32 msr = kvm_rcx_read(vcpu);

	bool handled;

	int r;



	switch (msr) {

	case APIC_BASE_MSR + (APIC_ICR >> 4):

		handled = !handle_fastpath_set_x2apic_icr_irqoff(vcpu, data);

		if (!lapic_in_kernel(vcpu) || !apic_x2apic_mode(vcpu->arch.apic) ||

		    kvm_x2apic_icr_write_fast(vcpu->arch.apic, data))

			return EXIT_FASTPATH_NONE;

		break;

	case MSR_IA32_TSC_DEADLINE:

		handled = !handle_fastpath_set_tscdeadline(vcpu, data);

		kvm_set_lapic_tscdeadline_msr(vcpu, data);

		break;

	default:

		handled = false;

		break;

	}



	if (!handled)

		return EXIT_FASTPATH_NONE;

	}



	kvm_vcpu_srcu_read_lock(vcpu);

	r = kvm_skip_emulated_instruction(vcpu);